Cannabis and mental health

Cannabis is an illegal drug which can affect your mental health. This page is about the affects that cannabis can have on your mental health. And how to get help and support. You may also find this page useful if you care for someone who uses cannabis.


  • Cannabis is known by different names such as marijuana and weed.
  • Cannabis is a drug that can make you feel happy or relaxed. And anxious or paranoid.
  • THC is the main chemical in cannabis which can change your mood and behaviour.
  • Skunk is the most common name for stronger types of cannabis which has more THC.
  • Research has found a link between cannabis and developing psychosis or schizophrenia.
  • Psychosis is when you experience or believe things that other people don’t.
  • Schizophrenia is the name of a mental illness. If you have schizophrenia, you can have psychosis and other symptoms.
  • If cannabis is affecting your health or how you feel, you can go to see your GP.


What is cannabis?

Cannabis is an illegal drug made from the cannabis plant. You can smoke or eat cannabis. You can smoke it on its own or mix it with tobacco to make a ‘joint’ or ‘spliff’. It can also be cooked in food or brewed in tea.

People use cannabis for different reasons. Sometimes they use it to relieve mental or physical symptoms. This is called self medication. It can appear to help short term but can increase problems or create new ones long term.

Cannabis is the most widely used illegal drug in Britain.1 But less people are using it than before.2 Young people are twice as likely to use it than older people.

Cannabis can be called marijuana, dope, draw, ganja, grass, hash, herb, pot, choof and weed. Stronger types of cannabis can be called skunk, super-skunk, Northern Lights, Early Girl and Jack Herer.

How does cannabis work?

Cannabis will go into your bloodstream when smoked. It will quickly be carried to your brain and stick to your receptors. This will have an effect on your mood and behaviour.

Cannabis contains lots of different chemicals known as cannabinoids. Some examples are cannabidiol (CBD) and tetrahydrocannabinol (THC). THC is the main chemical that affects how your brain works.

Stronger varieties of cannabis such as skunk contain more THC. Skunk has about 2-3 time more THC than cannabis from 30 years ago. Evidence suggests that the effects of skunk are faster and stronger than milder cannabis.

CBD can lessen the unwanted psychoactive effects of THC such as hallucinations and paranoia. It can also reduce anxiety. This means that the effects of THC will be lower if there is more CBD in the plant.

How can cannabis make me feel?

The effects of cannabis can be pleasant or unpleasant. Most symptoms will usually last for a few hours. But some unpleasant symptoms of cannabis can stay in the body for a few weeks.


Cannabis can make you feel happy, relaxed, talkative or laugh more than usual.  You may find that colours are more intense and music sounds better. Pleasant effects are known as a ‘high.’


Cannabis can cause anxiety attacks, hallucinations, depersonalisation, make you feel anxious, aggressive, paranoid, delusional and disorientated.  You might find it harder to concentrate or remember things. You may find that you cannot sleep well and you feel depressed. You may also feel hungry or like time is slowing down.

If you use cannabis for a long period of time you might feel depressed and have lower motivation.

Cannabis can affect how you sense things. You may see, hear or feel things differently. This is known as hallucinating. Hallucinations can be a sign of psychosis.

Psychosis can be a symptom of mental illness, including schizophrenia, schizoaffective and bipolar disorder. These can be called ‘psychotic illnesses.’

Can cannabis affect my mental health?

It is widely accepted that cannabis use can cause short term psychotic episodes.  But there is research to show that cannabis use can cause severe mental health problems, such as schizophrenia, bi-polar and psychosis. Most research seems to have a focus on the link between psychosis and cannabis, and schizophrenia and cannabis. But there is no definite evidence that cannabis causes psychotic illnesses.

Cannabis may be one of the causes of developing a mental illness but it is not be the only cause for many people. Not everyone who uses cannabis will develop psychosis or schizophrenia. Not everyone who has psychosis or schizophrenia has used cannabis. But you are more likely to develop a psychotic illness if you smoke cannabis. And are ‘genetically vulnerable’ to mental health problems. 

‘Genetically vulnerable’ means that you are naturally more likely to develop a mental health problem. For example if people in your family have a mental illness, you may be more likely to develop a mental health problem. But it doesn’t mean that you will.

Researchers studied a group of 18-20 year olds who smoked cannabis. When researchers followed them up more than 15 years later they found that participants were:

  • more likely to develop psychosis if they used skunk instead of milder cannabis,
  • 2 times more likely to develop schizophrenia than someone who doesn’t take cannabis, and
  • 6 times more likely develop schizophrenia if they are a heavy cannabis user compared to someone who doesn’t take cannabis.

Different research studies found the following.

  • Long term use can have a small but permanent effect on how well you think and concentrate. 
  • Smoking cannabis can cause a psychotic relapse if you have a psychotic illness.
  • You are more likely to develop depression and anxiety in young adulthood if you smoke cannabis from an early age.
  • You are more likely to get psychosis if you start using cannabis in your youth.

Cannabis may affect young people more because their brains are still developing up until the age of 20.

What is the difference between psychosis and schizophrenia?

Psychosis and schizophrenia are not the same illness.

Psychosis is the name of a symptoms or experiences, which include hallucinations and delusions. Hallucinations make someone experience things that other people are not. This might be seeing things or hearing voices. Delusions are when people have unusual beliefs that other people don’t have. 

Schizophrenia is a mental illness that affects how someone thinks or feels. Symptoms of schizophrenia include hallucinations and delusions. But often it will have other symptoms like feeling flat or emotionless, or withdrawing from other people.

The links below can give you more information about these two conditions: 

Is cannabis addictive?

Yes it can be. You are more likely to become dependent or addicted to cannabis if you have used it for a long time. Or use it everyday It is estimated that 17% of adult users who started using cannabis in their teens will become addicted. 9% of adult users who started using cannabis in adulthood will become addicted to cannabis.

You may find that your body starts to get used to the drug so you need more of it to get the same effects. This is called building up a tolerance.

If you become dependent or addicted, you may feel withdrawal symptoms when you don’t use cannabis. For example, you might:

  • be irritable,
  • have mood problems, such as depression and anxiety
  • have sleep problems,
  • not eat as much as usual,
  • be restless, and
  • be physically uncomfortable.

These symptoms are most difficult to deal with about a week after non cannabis use. They can last for up to 2 weeks.

How can I get help if cannabis is affecting my health?

Your GP

Speak to your GP if cannabis use is affecting your physical or mental health. Be honest with your GP about your cannabis use and symptoms. Your GP may not offer you the right support if they don’t know the full picture.

Your GP should refer you to a secondary care mental health service if you have psychosis or they think you have psychosis. A secondary care mental health service could be the community mental health team or an early intervention service.

You will not be excluded from mental health care because of cannabis misuse. You will not be excluded from a substance misuse service because of psychosis. Both psychosis and schizophrenia can be treated using antipsychotic medication and talking treatments.

Substance misuse service

They can offer counselling, support groups, advice and aim to help you to:

  • stop using cannabis,
  • reduce the affect that cannabis has on your life, and
  • support you to not start using again.

The service may be provided through the NHS or through charities. You can use a search engine such as Google to see what service is available in your area.

You may be able to self refer to this type of service. If you can’t self refer speak to your GP or health professional.

What about confidentiality?

You might be worried about telling your GP or other health professional that you are using cannabis. But health professionals will not be able to tell other people or services about what you have told them because of confidentiality laws. They can only tell other people about what you have said if:

  • there is a risk of serious harm to you or to others, or
  •  there is a risk of a serious crime.

For example, if you tell your doctor that you are planning to hurt yourself or other people, the doctor could decide to share this information with someone, or contact the police.

Our website uses cookies

Find out more in our privacy policy and cookies policy