How Does PCP Change Your Behaviour

PCP, short for phencyclidine, is a drug that changes how the brain works, and because the brain controls behaviour, the changes in behaviour can be wide and serious. PCP is called a dissociative drug, which means it disconnects a person from their own body and from the world around them. Under its influence, ordinary things can feel strange or unreal, time can feel distorted, and the person may struggle to tell what is real from what is not. That disconnection shows in how they act: in what they say, how they treat the people around them, the risks they take, and the choices they make. The change is not always sudden or dramatic. Often it creeps in slowly, so that family and friends notice it before the person using the drug does.

Behaviour is the most visible part of drug harm. A person can hide a lot of what is happening inside their body, but they cannot easily hide how they act at home, at work, or with friends. When PCP changes behaviour, the effects reach far beyond the person taking it. Partners feel frightened or confused. Parents watch a son or daughter become someone they barely recognise. Colleagues notice missed deadlines and strange moods. Friends drift away. The drug does not only change the brain. It changes relationships, trust, work, and daily life, and those changes can last long after the drug itself has worn off.

This article explains, in plain words, how PCP changes behaviour: what it does to thinking and feeling, why risk-taking and aggression can appear, how personality can shift over time, and how work, family and trust are affected. It is general information only, not individual medical advice. It does not explain how to use, make or obtain PCP, and it does not give doses or instructions of any kind. If you are worried about your own behaviour or someone else’s, a qualified health professional is the right person to talk to.

What PCP Does to Thinking and Feeling

PCP works by blocking a chemical messenger system in the brain that helps with learning, memory and the sense of what is real. When that system is blocked, the brain cannot process information in its normal, orderly way. Thoughts become jumbled. A simple conversation can be hard to follow. The person may lose track of what they were saying halfway through a sentence, forget what they were doing, or struggle to understand instructions that would normally be easy. This is not ordinary forgetfulness. It is the brain’s basic machinery being disrupted, and it shows up as confusion, poor concentration and muddled thinking.

Feelings are affected just as strongly. PCP can make a person feel detached, as if they are watching their own life from a distance rather than living it. Some people feel numb, as if nothing matters very much. Others feel intensely anxious or frightened for no clear reason. Mood can swing quickly, from calm to angry to tearful, without anything in the outside world changing. Because the drug also reduces the sense of pain, the person may not notice when they are hurt, tired or ill, and they may keep pushing themselves when their body needs rest. That combination of muddled thinking and unstable feeling is the foundation for most of the behaviour changes that follow.

Over time, repeated use makes these effects harder to shake off. The brain adapts to the drug, and it can take longer to return to normal after each use. Some people find that their thinking stays foggy even on days when they have not taken PCP, that their memory is worse than it used to be, or that they feel flat and low for long periods. This is not a sign that the person has become lazy or careless. It is a sign that the brain has been repeatedly disrupted and needs time, and often professional support, to recover. The longer the use continues, the harder that recovery becomes, and the more the behaviour changes settle into everyday life.

Why the Person Family Knew Changes

Families often describe the change in the same way: the person they knew seems to have been replaced by someone else. A son who was warm and talkative becomes withdrawn and secretive. A partner who was patient becomes irritable over small things. A friend who was reliable stops turning up, stops answering messages, and stops caring about plans that once mattered to them. These changes rarely happen in a single day. They build up gradually, a little at a time, so that each change on its own seems small, but together they add up to a person who feels like a stranger.

Part of the reason is that PCP changes how the person sees themselves and other people. When the brain cannot judge what is real, it becomes harder to read other people’s feelings, to understand why someone is upset, or to see a situation from another person’s point of view. A worried question from a parent can feel like an accusation. A gentle suggestion from a partner can feel like an attack. The person may become suspicious of the people closest to them, convinced that others are talking about them, plotting against them, or trying to control them. That suspicion is not a rational belief they have chosen. It is a product of a brain that is misreading social signals, and it makes close relationships very hard to maintain.

Another part is that the drug changes what the person cares about. As use becomes more regular, more time, money and thought go towards obtaining and using PCP, and less goes towards everything else. Hobbies are dropped. Friendships that do not involve the drug fade. Family occasions are missed or attended in a dazed, distant state. This is not because the person has stopped loving their family. It is because the drug has narrowed their world, so that the next use matters more than anything else. Families often find this the hardest change to understand, because it looks like selfishness from the outside. From the inside, it is the drug reshaping what the brain treats as important, day after day.

Risk-Taking Grows Bolder

One of the most dangerous behaviour changes linked to PCP is a sharp rise in risk-taking. The drug reduces fear, dulls pain, and weakens the brain’s ability to weigh consequences. A person who would normally stop at the edge of a roof, slow down on a dangerous road, or walk away from a fight may, under PCP, do the opposite. They may climb, run into traffic, drive while confused, or pick a fight with someone far stronger than them. They may believe they are invincible, or that they can fly, or that nothing can hurt them. These are not brave decisions. They are decisions made by a brain that can no longer judge danger.

Risk-taking also shows in quieter ways. A person may spend money they cannot afford, borrow money they cannot repay, or take chances with their job, such as turning up intoxicated or disappearing for days. They may have unprotected sex, share needles, or take other drugs without thinking about the risks. They may agree to things they would refuse when clear-headed, or trust people they would normally avoid. Each of these choices carries its own consequences, from debt to disease to arrest, and each one adds to the damage that the drug is already doing to their life.

The reason this matters so much is that risk-taking under PCP can harm other people as well as the person taking the drug. A driver under the influence can kill a stranger. A fight started in a confused, agitated state can injure someone who had nothing to do with the drug. A parent who is intoxicated cannot look after a child properly. The behaviour is not contained within one person’s life. It spills outwards, into families, workplaces and streets, and that is why health professionals treat PCP-related risk-taking as a serious public safety issue, not just a private problem.

Personality Shifts Slowly

Personality does not usually change overnight, but PCP can shift it gradually, in ways that are hard to reverse. The most common shift is towards withdrawal and flatness. A person who was once lively and interested in the world becomes quiet, uninterested and hard to reach. They may sit for hours staring at nothing, answer questions with one word, or show little reaction to good news or bad news. This flatness is not calm. It is the brain struggling to feel anything clearly, and it can be mistaken for depression, laziness or rudeness by people who do not know what is causing it.

Another common shift is towards irritability and suspicion. Small frustrations that the person once brushed off now provoke anger. A delayed bus, a question asked twice, a disagreement over something trivial can trigger an outburst that seems out of all proportion. The person may become convinced that others are against them, that colleagues are plotting, or that family members are spying on them. These beliefs feel completely real to the person holding them, which is why arguing against them rarely helps. The problem is not a stubborn opinion. It is a brain that is generating false conclusions and treating them as facts.

A third shift is towards impulsiveness. The person may act on the first thought that comes into their head, without pausing to think it through. They may quit a job on a whim, end a relationship in anger, spend a month’s wages in a day, or walk out of the house in the middle of the night. Afterwards, they may not fully understand why they did it, or they may feel ashamed and confused by their own actions. This impulsiveness is frightening for the person themselves, because they can feel their own judgement slipping away, and it is frightening for those around them, because they never know what will happen next.

Aggression Appears Without Warning

Aggression is one of the most feared effects of PCP, and it is also one of the most misunderstood. Not everyone who takes PCP becomes aggressive, and aggression is not the only behaviour change it causes. But when it does appear, it can be sudden, intense and frightening, and it can be triggered by very little. A person may become aggressive because they are terrified by a hallucination, because they believe someone is attacking them, because they are confused and cannot understand what is happening, or because the drug has removed the normal brakes that stop anger turning into violence. The aggression is real, and it can cause real harm, but it is driven by fear and confusion far more often than by cruelty.

The unpredictability is what makes it so hard for families to live with. A person can be calm one minute and furious the next, with no clear reason for the change. A family member may learn to watch for warning signs, to keep their voice low, to avoid sudden movements, and to leave the room when the mood shifts. Children in the home may become anxious, withdrawn, or afraid to come home. Partners may feel they are walking on eggshells in their own house. This is not a normal family life. It is a household organised around the fear of the next outburst, and that fear itself does lasting damage to everyone in it, especially children.

It is important to be clear about safety here. If someone under the influence of PCP becomes aggressive, the priority is to get to safety and call for help, not to argue, restrain them by force, or try to talk them down if that puts you in danger. A person in this state is stronger than usual because they cannot feel pain and their normal limits are switched off, and struggling with them raises their temperature and heart rate, which can be dangerous for them as well. Move away, keep a safe distance, call emergency services, and let trained staff handle the situation. Protecting yourself is not abandoning the person. It is the only way to make sure both of you survive the moment.

Work, Study and Daily Duties Slip

PCP use damages the ability to work and study in a very practical way. Concentration becomes harder. Memory becomes less reliable. A person may forget instructions, miss deadlines, or make mistakes they would never have made before. They may turn up late, or not turn up at all, and when they do turn up, they may be dazed, irritable or unable to focus. Over weeks and months, this adds up. Employers notice. Teachers notice. Colleagues who once relied on the person start to work around them instead. A job that was secure becomes uncertain, and a course of study that was going well starts to fall apart.

Daily duties slip in the same way. Bills go unpaid, not because there is no money, but because the person cannot organise themselves to pay them. Appointments are missed. The house becomes untidy. Meals are skipped or eaten at strange hours. Sleep becomes irregular, with long periods awake followed by long periods of heavy, unrefreshing sleep. A parent may forget to collect a child from school, or be too intoxicated to look after them safely. These are not small lapses. They are the basic tasks of adult life becoming too hard to manage, and each failure makes the next one more likely, because debt, warnings at work, and tension at home add stress that pushes the person further towards the drug.

The loss of work or study is not just a financial problem. Work gives a person structure, purpose, and a reason to get up in the morning. Study gives them a future to work towards. When those are lost, the person’s world narrows further, and the drug becomes an even bigger part of what is left. That is why support for someone using PCP often needs to include practical help as well as medical help: help to keep a job, to return to study, to manage money, and to rebuild the daily routines that make a normal life possible. Without that, even a person who wants to stop can find it very hard to see what they are stopping for.

Secrets, Lies and Broken Trust

As PCP use becomes more regular, secrecy often grows around it. The person may hide where they have been, who they were with, and how much money they have spent. They may lie about why they were late, why they look unwell, or why they need money. At first, the lies may be small and easy to tell. Over time, they become a habit, and then a necessity, because the truth would mean admitting the scale of the problem and facing the consequences. Family members often sense that something is wrong long before they know what it is, and that sense of being lied to is deeply painful, even when the lies are clumsy and obvious.

Trust breaks down on both sides. The family stops believing what the person says, and the person stops believing that the family will understand or help. Conversations become arguments. Questions feel like interrogations. Offers of help feel like attempts to control. The person may withdraw further, spending more time away from home, with people who do not ask questions, because that feels easier than facing the people who care about them most. This withdrawal is tragic, because the family is often the best source of support the person has, and the drug is pushing them away from it at exactly the moment they need it most.

Rebuilding trust after this damage takes a long time, and it cannot be rushed. It requires honesty, consistency, and a willingness to keep promises, even small ones, over weeks and months. A person who says they will be home at a certain time and is home at that time, who says they will attend an appointment and attends it, who says they will not use the drug and does not use it, is slowly showing their family that they can be relied on again. It is slow work, and it is painful work, but it is possible, and it is one of the most important parts of recovery. Trust is not rebuilt by a single apology. It is rebuilt by a pattern of behaviour that proves, day after day, that change is real.

Behaviour Is the Visible Harm

Behaviour is the part of PCP harm that other people see first, and it is often the part that finally pushes a family to seek help. A person can hide a lot about their health, but they cannot hide the fact that they have become aggressive, secretive, unreliable, or frightening to be around. That visibility is both a burden and an opportunity. It is a burden because it exposes the person to judgement, shame and conflict. It is an opportunity because it means the problem cannot be ignored forever, and because the people who see the change are often the people best placed to encourage the person to get help.

It is worth remembering that behaviour change is a warning sign, not a verdict on the person’s character. A person who has become aggressive, dishonest or unreliable under the influence of PCP is not necessarily a bad person. They are a person whose brain is being repeatedly disrupted by a powerful drug, and whose judgement, empathy and self-control are being undermined by that disruption. That does not excuse harm caused, and it does not mean other people should accept being hurt or frightened. But it does mean that blame alone will not fix the problem. What fixes it is stopping the drug, getting support, and giving the brain time to heal, so that the person’s real character has a chance to come back.

The most hopeful thing to say about behaviour change is that it can improve. When a person stops using PCP and stays away from it, thinking usually becomes clearer, mood becomes more stable, and relationships begin to heal. It does not happen overnight, and it does not happen without effort, but it does happen, and families who have lived through the worst of it often say that the return of the person they knew is the most rewarding part of recovery. The person who was lost to the drug is still there, underneath the confusion and the anger, and with time, support and patience, they can come back. That is why it matters to keep trying, even when the behaviour feels hopeless, and even when the person themselves has given up on change.

Improvement often shows in small signs before it shows in big ones. A person may start remembering appointments again, or answering the phone when family call, or showing interest in a meal, a walk, or a conversation. They may apologise without being asked, or notice when someone else is upset, or make a plan and keep it. These moments may seem ordinary, but to a family that has lived with unpredictability for months, they are enormous. They are evidence that the brain is healing and that empathy and judgement are returning. Noticing and naming these small improvements matters, because it encourages the person to keep going, and it reminds the family that the effort is working, even when progress feels slow.

It is also important to be honest that recovery is rarely a straight line. A person may improve for weeks and then have a bad day, a setback, or a return to use. That does not erase the progress they have made, and it does not mean they have failed for good. It means recovery is hard, and that the person needs support to get back on track rather than blame for slipping. Families who understand this, and who can respond to a setback calmly rather than with anger or despair, give the person the best chance of trying again. The goal is not perfection. It is steady, sustained improvement over time, with help when it is needed, and with the understanding that the person underneath the behaviour is worth the effort.

My Take:

I think behaviour is where the harm of PCP becomes impossible to ignore, and that is why this topic matters so much to me. A person can keep the physical effects of a drug private for a long time. They cannot keep their behaviour private. The way they speak to their partner, the way they treat their children, the way they turn up at work, the way they spend money, the way they disappear for days, all of that is visible, and all of it affects other people. When I think about PCP, I do not only think about the brain chemistry. I think about the kitchen table where a family sits in silence because they do not know which version of the person will come home tonight. That silence is the real cost, and it is paid by people who never took the drug at all.

What strikes me most is how slow the change can be, and how that slowness makes it harder to act. If a person changed completely in a single day, everyone around them would know something was seriously wrong and would seek help at once. But PCP often changes a person a little at a time. A missed appointment here, a sharp word there, a night out that lasts too long, a promise broken and then another one. Each incident on its own can be explained away, forgiven, or forgotten. It is only when you step back and look at months of them together that the pattern becomes clear, and by then the damage to trust and relationships is already deep. I think families should trust that pattern. If the person you love is becoming someone you do not recognise, that is not your imagination. It is a warning, and it deserves to be taken seriously.

I feel strongly about the way we talk about aggression linked to PCP, because I think the usual conversation misses the point. People hear that PCP can make someone violent, and they picture a monster. I picture a frightened, confused person whose brain is telling them that they are in danger, that the people around them are threats, and that they need to fight to survive. That does not make the aggression acceptable, and it does not mean anyone should stay in a room with someone who is dangerous. But it does mean the person is ill, not evil, and that the right response is medical help and safety, not punishment and rejection. I would rather see a person get treatment than see them written off as a lost cause, because writing people off helps no one and saves no one.

The risk-taking worries me in a different way, because it is so often treated as a joke or as a sign of boldness. A person who climbs onto a roof, drives too fast, or picks a fight while under the influence is not being brave. They are being robbed of their judgement by a drug that has switched off the part of the brain that says stop. That loss of judgement can kill them, and it can kill someone else who was simply in the wrong place at the wrong time. I think we need to be much clearer about this, especially with young people. PCP does not make you fearless in a good way. It makes you unable to feel fear when fear is the only thing keeping you alive. That is not strength. It is a chemical trick, and it is a trick that has ended lives.

Trust is the part of this I keep returning to, because trust is so hard to build and so easy to destroy. A family can spend years building a relationship based on honesty, and PCP can wear it away in months with a steady stream of small lies, missed promises and unexplained absences. The person using the drug often does not mean to lie in a cruel way. They lie because the truth would mean admitting how bad things have become, and that admission feels unbearable. But the family experiences the lies as betrayal, and that betrayal leaves a wound that does not heal just because the drug stops. Rebuilding trust takes time, consistency, and a willingness to be honest even when honesty is painful. I think anyone going through that process deserves patience, and I think the family deserves support too, because they have been hurt as well.

I also think about children in these households, because they are the ones with the least power and the most to lose. A child who grows up with a parent whose behaviour changes unpredictably learns to be watchful, anxious and careful in their own home. They learn to read moods, to stay quiet, to avoid drawing attention to themselves. That is not a childhood. That is survival, and it leaves marks that last into adulthood. I do not say this to blame parents who are struggling with drug use. I say it because children need to be part of the conversation, and because protecting them has to be a priority, even when the adult in the house is the one who needs help. A child should never have to manage an adult’s drug use. That is not their job, and it is not fair to ask it of them.

Work is another area I think about, because losing a job is often the moment when everything else falls apart. A person can cope with a lot of strain at home, but once they lose their income, the stress multiplies. Rent becomes hard to pay. Debt grows. Shame grows with it. The person has less structure in their day, less reason to get up in the morning, and more time to spend thinking about the drug. I think employers and colleagues have a role here too, not to excuse poor work, but to notice when a reliable person suddenly becomes unreliable, and to ask, kindly and privately, whether something is wrong. That question, asked at the right moment, can be the first step towards help. Silence, on the other hand, helps no one.

I do not believe that telling people to simply stop using PCP is enough, and I think anyone who has watched someone struggle with it knows why. The drug changes the brain in ways that make stopping very hard, and it changes the person’s life in ways that make stopping feel pointless. If you have lost your job, damaged your relationships, and lost trust in yourself, what are you stopping for? That is why I think support has to be practical as well as medical. Help with work, with housing, with money, with daily routines, with rebuilding relationships, all of that matters. A person needs a life worth returning to, not just a lecture about why the drug is bad. The lecture they have already heard. The life is what they have lost.

There is a question I am often asked, in different forms, which is whether the person who has changed so much can ever come back. I believe they can, but I will not pretend it is quick or easy. The brain needs time to recover from repeated disruption, and relationships need time to heal from repeated hurt. Some changes may linger. Memory may not return fully. Trust may take years to rebuild. But I have seen enough to know that people do recover, that they do become recognisable to their families again, and that the return of the person they knew is one of the most powerful motivations to keep going. If you are a family member reading this and feeling hopeless, I would ask you to hold on to that. The person you love is still there, underneath the confusion and the anger, and they need you to believe that even when they cannot believe it themselves.

I want to say something about the families as well, because they are often forgotten in all of this. Living with someone whose behaviour has changed because of PCP is exhausting, frightening and lonely. Family members may feel guilty, as if they should have stopped it sooner. They may feel angry, and then guilty for feeling angry. They may feel ashamed, and hide the problem from friends and neighbours, which makes them even more isolated. All of those feelings are normal, and none of them are a sign of failure. If you are in that position, I would urge you to seek support for yourself, not just for the person using the drug. You cannot help someone else if you are running on empty, and you deserve help in your own right, not only as a carer.

I also think it is worth talking about apologies, because they come up so often in this situation and they are so often misunderstood. A person who has hurt their family while using PCP may say sorry, and mean it, and still repeat the same behaviour the next week. That does not necessarily mean the apology was a lie. It means an apology on its own is not enough to change a brain that is still being affected by the drug. Real change shows in actions, not words: turning up when promised, staying away from the drug, attending appointments, being honest about setbacks. Families learn to listen less to what is promised and more to what is done, and that is a painful but sensible way to protect themselves. If you are the person apologising, the best apology you can give is a pattern of changed behaviour, sustained over time, even when no one is watching.

Boundaries are another subject I feel strongly about, because families are often told to be endlessly patient, as if patience alone will fix the problem. Patience matters, but it is not the same as having no limits. A family has every right to say that violence, theft, or drug use in the home is not acceptable, and to protect children, money, and their own safety. Setting a boundary is not the same as abandoning the person. It is a clear statement of what is needed for the relationship to continue, and it can be the thing that finally makes the person realise how serious the situation has become. Boundaries work best when they are calm, consistent, and explained in advance, rather than shouted in anger during a crisis. They are not a punishment. They are a form of care, for the family and for the person using the drug.

Professional help deserves a mention too, because behaviour change on this scale is rarely something a person can fix alone, however strong their willpower. A health professional can assess how the drug has affected thinking and mood, talk about treatment options, and help the person build a plan that covers not just stopping the drug, but rebuilding the parts of life the drug has damaged. Support groups, counselling, and practical help with work or housing can all play a part, and none of them are a sign of failure. Asking for help is not weakness. It is the recognition that a powerful drug has changed the brain in ways that need expert support to undo, and that the person deserves that support as much as anyone else with a serious health problem.

One last thought stays with me, and it is about how easy it is to give up on a person whose behaviour has become difficult. Friends drift away, colleagues stop trying, and even family members can reach a point where they feel they have nothing left to give. I understand that exhaustion, and I do not judge it. But I think it is worth remembering that the person underneath the behaviour did not choose to become this way in a single decision, and that they may not be able to find their way back without someone still believing that they can. That belief does not have to be loud or constant. It can be a phone call, a visit, a message that says you are still there. Small acts of connection can matter enormously to someone who feels that everyone has given up on them, and they cost very little to give.

Finally, I would say this to anyone who recognises their own behaviour in this article. If you have noticed that you are more irritable, more secretive, more reckless, or more withdrawn than you used to be, and you think PCP might be part of the reason, that noticing is important. It is not a confession. It is not a verdict. It is the first step towards change, and it takes honesty to get there. Talk to someone you trust, or to a health professional, about what you have noticed and what you want to be different. You do not have to fix everything at once. You have to start, and starting is enough. The person you were before the drug changed you is not gone. They are waiting, and they are worth coming back to.

Frequently Asked Questions

How does PCP change behaviour?

PCP changes behaviour by disrupting the brain’s ability to think clearly, judge danger, read other people’s feelings, and control impulses. A person may become confused, detached, irritable, suspicious, or impulsive. They may take risks they would normally avoid, become aggressive without warning, withdraw from family and friends, and struggle with work and daily duties. These changes can appear during use and, with repeated use, can linger even on days when the person has not taken the drug.

Can PCP cause reckless behaviour?

Yes. PCP can cause reckless behaviour because it reduces fear, dulls pain, and weakens the brain’s ability to weigh consequences. A person may drive dangerously, climb to unsafe places, start fights, spend money they cannot afford, or take chances with their safety and the safety of others. They may believe they are invincible or that nothing can hurt them. This is not bravery. It is a loss of judgement caused by the drug, and it can lead to serious injury or death for the person and for people nearby.

How does PCP affect work behaviour?

PCP affects work behaviour by damaging concentration, memory and reliability. A person may forget instructions, miss deadlines, make mistakes, turn up late or not turn up at all, and struggle to focus when they are present. Over time, this can lead to warnings, lost shifts, or losing a job altogether. Daily duties at home slip in the same way, with bills unpaid, appointments missed, and household tasks left undone. Losing work also removes structure and purpose, which can make the drug problem worse.

Why does PCP change personality?

PCP changes personality because it repeatedly disrupts the brain systems that control mood, thinking, empathy and self-control. Over time, a person may become withdrawn and flat, or irritable and suspicious, or impulsive and unpredictable. These shifts build up gradually, so family members often notice them before the person does. The changes are not a sign that the person has become a bad person. They are a sign that the brain has been repeatedly affected by the drug, and that it needs time and support to recover.

Can PCP make a person aggressive?

Yes, PCP can make a person aggressive, although not everyone who takes it becomes aggressive. Aggression can appear suddenly and be triggered by fear, confusion, hallucinations, or a false belief that someone is a threat. The drug also removes the normal brakes that stop anger turning into violence, and reduces the sense of pain. If someone becomes aggressive under the influence of PCP, the priority is to move to safety and call emergency services, not to argue or try to restrain them by force.

Does PCP make people secretive?

Yes, PCP use often leads to secrecy. A person may hide where they have been, who they were with, and how much money they have spent, and may lie about being late, looking unwell, or needing money. At first the lies may be small, but over time they become a habit, because the truth would mean admitting the scale of the problem. This secrecy damages trust on both sides and pushes the person further away from the family and friends who could help them most. Rebuilding trust takes honesty and consistency over a long period.

Sources

This article is general information only. It is not individual medical advice. If you are worried about your health, talk to a qualified health professional.