Personality Disorders and Substance Use: When Mood, Relationships, and Substances Collide

Written by the medical team at Day One Rehabilitation Center, Nakhon Nayok, Thailand · Medically reviewed by Dr. Pichayut Kasemphakdeephong (Psychiatrist)

Rapid mood swings, frequent conflict with people close to them, a quick temper, impulsive decisions, fear of abandonment, distrust of others, or repeated risky behavior are things families may notice in someone who is using substances. But these behaviors don’t always mean the person has a “personality disorder.”

Substances can dramatically change mood, decision-making, and behavior. Yaba and crystal meth (ice) can cause irritability, restlessness, or paranoia. Alcohol can lower inhibitions to the point of impulsive behavior. And withdrawal from certain substances can cause mood swings, anxiety, and insomnia.

On the other hand, some people have had a long-standing pattern — going back to adolescence or early adulthood — of difficulty managing emotions, a troubled sense of self, and problematic relationships with others. When faced with stress, conflict, a feeling of emptiness, or fear of being abandoned, they may start using alcohol or other substances to temporarily ease those feelings, which can then develop into an addiction.

Treatment shouldn’t be quick to label someone as “having a bad character” or “unable to change.” Instead, it needs to understand which behaviors are long-standing patterns, which are related to the substance, and whether any other psychiatric condition is also present. Once the underlying causes are clearer, treatment for both the personality issue and the addiction can be planned more precisely.

What Is a Personality Disorder, and How Is It Different From Ordinary Temperament?

Everyone has a different personality. Some people are quiet, some are outgoing, some are very cautious, while others make decisions quickly. These differences aren’t a disorder simply because they’re different from other people.

In medical terms, “personality disorder” refers to a fairly long-standing pattern of thinking, emotion, behavior, and relationships that clearly deviates from what’s appropriate for the context, and that causes distress or problems in daily life, work, or relationships.

The key point is that these patterns usually didn’t just appear over the past few days or after substance use began — they have typically been continuous since adolescence or early adulthood and show up across many different situations.

There are many types of personality disorders, so symptoms can vary widely, such as:

Difficulty controlling emotions, with intense mood swings
Unstable relationships or frequent conflict with people close to them
Intense fear of abandonment
A chronic feeling of emptiness or an unstable sense of self
Impulsivity and making decisions without considering long-term consequences
Excessive distrust or suspicion of other people’s intentions
Avoiding relationships out of fear of rejection or criticism
An intense need for approval from others
Rigid thinking or behavior patterns that are hard to adapt and that affect daily life
Risky behavior or, in some cases, self-harm

Having some of these symptoms doesn’t mean a diagnosis can be made right away — especially in someone who is currently using substances, experiencing withdrawal, severely sleep-deprived, or in the middle of a mood episode.

Diagnosis therefore requires a long-term history and evaluation by a specialist. The term “personality disorder” shouldn’t be used simply to label someone whose behavior a family dislikes or finds hard to manage.

Why Might Personality Disorders Co-Occur With Substance Addiction?

The relationship between personality problems and substance use can take many forms, and it doesn’t mean that everyone with a personality disorder will become addicted.

In some people, impulsivity makes it easy to decide to try a substance or go back to using once a craving hits. In others, intense and quickly shifting emotions mean that when they feel angry, hurt, rejected, or afraid of being abandoned, they may use a substance to bring those feelings down immediately.

Some feel empty or unsure of who they are, so they use alcohol or other substances to feel better temporarily. Some feel very anxious around other people, so they drink to feel brave enough to speak up or socialize more easily.

Substance use can then start to function as a quick way of managing emotions — feeling very stressed, fighting with someone close, or feeling abandoned, and using the substance to lighten that feeling. Once the substance helps them feel better temporarily, the next time a similar emotion arises they’re more likely to reach for the same solution again.

As this repeats more often, the person may become more dependent on the substance. At the same time, the effects of the substance can make it even harder to control emotions and behavior, leading to conflict, damaged relationships, financial problems, or guilt — which in turn can become a new stressor that triggers using again.

Treatment therefore needs to help build ways of managing emotions and relationships that don’t rely on the substance as the primary method.

How Can You Tell Whether It’s a Personality Problem or Behavior Change From Substance Use?

This is a point that requires care, because substance use can make someone appear very different from their usual self.

For example, someone using yaba or crystal meth continuously may become irritable, unable to sleep, short-tempered, paranoid, or even experience psychotic symptoms. When a family sees this, it may feel like the person “has turned into someone else,” but it doesn’t mean they have a personality disorder.

Alcohol can lower inhibitions, leading to quick decisions and saying or doing things that would normally be held back — so behavior while intoxicated shouldn’t be used on its own to diagnose a personality disorder.

Withdrawal, stress, sleep deprivation, depression, bipolar disorder, ADHD, PTSD, and other psychiatric conditions can also cause mood swings, impulsivity, or relationship problems.

The treatment team therefore needs to look back at how long the behavior pattern has been going on, whether the same pattern existed before substance use began, whether it shows up across multiple relationships and situations, and how the symptoms change during periods without substance use.

Some people had personality problems first and then started using substances. Some have behavior changes purely from the substance without any underlying personality disorder. And some genuinely have both problems occurring together.

Clearly distinguishing the cause matters more than rushing to name a diagnosis, because the treatment plan differs for each case.

How Is a Personality Disorder Treated When It Co-Occurs With Addiction?

Treatment doesn’t aim to change who a person fundamentally is — it aims to reduce patterns of thinking, emotion, and behavior that cause distress or create recurring problems, while building new skills for managing emotions and relationships.

Assessing Both Personality and the Effects of the Substance Before Reaching a Diagnosis

In someone who uses substances continuously, the assessment must carefully track the timing of symptoms. If the person is currently intoxicated, in withdrawal, sleep-deprived, or experiencing severe psychotic symptoms, these may need to be stabilized first, with behavior patterns monitored over the following period.

Information from the family can help build the long-term picture — for example, whether the same kind of relationship problems existed before substance use began, whether impulsivity was present before, and whether these patterns have shown up across many periods of life or only changed after substance use started.

Learning to Manage Emotions Without Using Substances as an Immediate Escape

Someone who struggles to control emotions may feel that emotions arise so quickly and intensely that they have to do something about it right away. Using a substance can then become a fast way of dampening that feeling.

Therapy helps the person learn to notice their emotions before they intensify, recognize which situations act as triggers, and build safer ways of coping.

For certain types of personality disorder, therapy that focuses on emotional regulation skills, tolerating difficult feelings, communication, and building stable relationships can play an important role.

The goal isn’t to make emotions disappear — it’s to help the person be able to feel anger, sadness, disappointment, or fear without needing to use a substance or act in a harmful way every single time.

Treating the Addiction at the Same Time

If there is a clear addiction, treatment shouldn’t wait for the personality issue to fully resolve before starting to treat the addiction, because the substance itself can make emotional control, decision-making, and relationships worse.

The treatment team needs to help identify what events tend to precede a relapse — a fight with a partner, being rejected, feeling isolated, feeling empty, work stress, or anger at a family member.

Once these patterns become clearer, a relapse-prevention plan can be built, along with alternative ways of handling the same kinds of situations.

Motivational conversations are also valuable, especially for someone who isn’t yet sure whether they want to stop using. Arguing, forcing, or trying to win the point usually doesn’t build lasting motivation.

What Role Does Medication Play in Treatment?

In general, there is no medication that directly “changes a personality.” However, a psychiatrist may consider medication to treat co-occurring symptoms or conditions — depression, anxiety disorder, bipolar disorder, psychotic symptoms, or other issues — as clinically indicated.

For someone with a history of addiction, medication choices must also consider the risk of misusing the medication or becoming dependent on certain kinds of it.

So treatment doesn’t rely on medication alone — psychological therapy, skills training, structuring the environment, and relapse prevention are all critically important.

How Should Families Cope When a Personality Problem Co-Occurs With Substance Use?

Families can feel exhausted when the same cycle repeats — a severe fight, the person leaving the house, going back to using, then coming back to apologize, before the same thing happens again.

Understanding that there is an underlying psychological problem doesn’t mean the family has to accept every behavior. Compassion and clear boundaries can coexist.

Families should avoid using the diagnosis as an accusation — such as “you do this because you have a personality disorder” — because it can make the person feel that everything they do is being seen only through the lens of a diagnosis, which can reduce their willingness to engage in treatment.

It’s better to talk about observable behavior — for example, “Lately, every time we argue, you go out and drink or use, and the next day things are even harder. We want to help find a way to deal with anger or sadness without having to go back to using.”

The family’s boundaries should be clear and consistent, especially around money, bringing substances into the house, violence, damaging property, and behavior that puts others at risk.

If there are thoughts or behaviors of self-harm, threats to harm oneself or others, severe psychotic symptoms, or an inability to control behavior to the point of creating risk, safety must come first and an urgent evaluation should be arranged.

If the person isn’t ready for treatment yet, the family can consult a specialist first, to plan how to communicate and set appropriate boundaries, without needing to wait for the person to accept that they have every part of the problem first.

When Personality Problems Co-Occur With Substance Use, Where Should You Start Seeking Help?

If the main problem is about mood, relationships, or suspected personality disorder, and alcohol, cannabis, or other substances are only used occasionally without a clear pattern of addiction — or if the person isn’t ready for treatment yet and the family wants guidance first — a good place to start is a consultation at Piti Clinic, our outpatient mental-health clinic in Bangkok (Pradiphat Road, Saphan Khwai), to assess mental health, patterns of mood and relationships, and the connection between symptoms and substance use, and to help the family plan how to talk with the person and encourage them into appropriate treatment.

But if substance use is repeated and uncontrolled — used every time the person feels angry, stressed, empty, or has a relationship problem; increasing in amount; stopped and restarted multiple times; accompanied by withdrawal symptoms; or affecting work, finances, and family — then treating the addiction seriously needs to become the priority.

Especially for someone who is highly impulsive, struggles to control their emotions, and turns to the substance as soon as conflict arises, residential treatment can help create early distance from the substance and from triggering situations, while building emotional-regulation skills and addressing any psychiatric issues at the same time.

Treating Personality Disorders and Addiction at Day One Rehabilitation Center

For those with addiction alongside a personality problem, Day One Rehabilitation Center places importance on assessing patterns of substance use, mood, impulsivity, relationships, sleep, and any other co-occurring psychiatric conditions.

Residential treatment reduces access to the substance and to triggers in the early period, allowing the treatment team to track how mood and behavior change after stopping use, and which problems persist even without the influence of the substance.

A psychiatrist can distinguish between the effects of the substance, withdrawal, mood disorders, ADHD, PTSD, psychotic symptoms, and personality patterns, so treatment doesn’t become fixed on a single diagnosis.

Individual therapy helps the person understand their own triggers — feeling rejected, anger, loneliness, emptiness, or relationship conflict — and learn ways of coping that don’t rely on the substance.

Group therapy also provides a space to practice listening, communication, receiving feedback from others, managing conflict, and living alongside others within clear boundaries.

Relapse prevention prepares for real-life situations after leaving the center — how to handle a fight with a partner, who to contact if a craving arises after feeling rejected, or how to create space for oneself before acting when emotions are intense enough to want to act immediately.

The goal, then, is not to change “what kind of person” someone is, but to help them manage emotions, relationships, and decisions better, while reducing reliance on the substance as a way of coping with distress.

Frequently Asked Questions About Personality Disorders and Substance Use

Does having mood swings mean someone has a personality disorder?

Not always. Mood swings can be caused by stress, lack of sleep, substances, withdrawal, depression, bipolar disorder, ADHD, PTSD, and other conditions. Diagnosing a personality disorder requires looking at a long-term pattern, not just symptoms over a short period.

Does having a personality disorder mean someone is a bad person?

No. A medical diagnosis isn’t used to judge whether someone is a good or bad person. It’s used to describe patterns of thinking, emotion, and behavior that cause distress or affect daily life, and to help guide appropriate treatment.

Can drugs change someone’s personality?

Substances can change mood, decision-making, impulse control, sleep, and perception. Some people therefore behave very differently while using or during withdrawal, but that doesn’t always mean they have a personality disorder.

Can personality disorders be treated?

Yes, they can be treated, and the symptoms or problematic behaviors can improve. Psychological therapy is a key part of treatment, focused on developing emotional management, relationships, behavioral control, and ways of coping with stress.

Is there medication that treats personality disorders directly?

Generally, there is no medication used to directly change a personality. A psychiatrist may, however, use medication to treat co-occurring symptoms or psychiatric conditions as clinically indicated. Psychological therapy therefore remains a key part of treatment.

Some people with borderline personality disorder may have impulsivity, difficulty regulating emotions, fear of abandonment, or risky behavior, all of which can co-occur with a substance use problem. But diagnosis requires evaluation by a specialist — it shouldn’t be concluded from mood swings or relationship problems alone.

If someone uses a substance every time they fight with a family member, what should be done?

Both the pattern of substance use and what happens right before it should be assessed. Treatment helps the person recognize which emotions or situations trigger their cravings, and practice ways of handling conflict without needing to use every time.

If the person won’t admit they have a problem, what should the family do?

There’s no need to first get the person to accept a diagnosis by name. It can start instead from problems they themselves recognize — frequent conflict with people around them, insomnia, trouble at work, running out of money, or using every time they’re stressed — and then encourage them to get evaluated based on that problem.

If someone has both a personality disorder and an addiction, what should be treated first?

If there is a co-occurring addiction, both problems should be treated together. Safety, intoxication, withdrawal, and any severe psychiatric symptoms need to be managed first, followed by ongoing monitoring of mood, behavior, and relationship patterns. The addiction shouldn’t be treated while ignoring the psychological problem that’s driving the return to substance use.

Do personality disorders combined with substance use always require going to a treatment center?

Not for everyone. If the mental health condition is the main problem and substance use is only occasional without a clear pattern of addiction, a mental health evaluation can be a starting point. But if use is repeated and uncontrolled, if the substance is needed to manage emotions, if the person stops and relapses multiple times, if there are withdrawal symptoms, or if substance use is damaging their life, residential addiction treatment at Day One Rehabilitation Center should be seriously considered.

Treatment Doesn’t Change Who Someone Is — It Helps Them Cope With Life Better

The term “personality disorder” shouldn’t be used to judge someone as a bad person, selfish, out of control, or incapable of change. What matters more than the diagnosis is understanding which patterns of thinking, emotion, and relationships are causing distress, and how substance use has become entangled with those patterns.

For some people, the substance becomes the fastest way to manage anger, fear of abandonment, loneliness, emptiness, or stress. But with repeated use, it can create new problems in mood, finances, work, and relationships — making the very thing they were trying to escape even worse.

Appropriate treatment therefore has to address both the substance use problem and the mental health condition together — helping the person recognize their own triggers, develop emotional-regulation skills, communicate and build relationships better, and have a plan for coping when cravings arise.

Families don’t need to wait for the person to accept a diagnosis before seeking help. Starting from the real problems that are happening, and talking without using the diagnosis as an accusation, can open the door to treatment. And if substance use has become repeated and uncontrolled, treating the addiction seriously should happen alongside caring for the underlying psychological problem.