Cannabis and Your Mental Health

FAQs and information about cannabis and how it might affect your mental health

About this information sheet

This information sheet is for the public but particularly for young people who want to know about some of the potential harmful effects of using cannabis. Cannabis is known as ‘weed’, ‘blow’, ‘hash’, ‘dope’ and ‘grass’.

We answer 20 frequently asked questions about this drug under three headings.

  • Cannabis and its use in Ireland

  • The general risks of cannabis

  • Cannabis and mental health


View this information sheet as a PDF here.

  • More and more people are using cannabis in Ireland.
  • More and more young people are unaware of the harms of using cannabis.
  • Misleading information has increased the perception of cannabis as being harmless. But it is not harmless.
  • People who use the mental health services – both young people and adults – are more at risk of harm from cannabis use.
  • The number of young people with a cannabis-related medical diagnosis admitted to hospitals in Ireland tripled between 2005 and 2017.
  • It’s the mostly commonly used illegal drug in Ireland.
  • It’s easily available.
  • Cannabis bought now is much stronger (more potent) than it was years ago.
  • It has harmful effects on mental health.
  • Cannabis is not a treatment for mental illness.
  • Young people who use cannabis regularly are at highest risk of mental health harms.
  • It is addictive, and more addictive in young people.
  • Using cannabis is linked with problems in school, work and family.

The questions we answer:

Section 1: Cannabis and its use in Ireland

Cannabis is the most widely and regularly used illegal drug in Ireland.

However, other substances, such as tobacco in cigarettes or alcohol are more commonly used. These substances are not illegal to sell in Ireland.

These facts come from two big surveys performed in Ireland. The first survey was a survey of 10,000 households on the island of Ireland that was conducted in 2015. This survey included people aged 15 and older and was called the National Advisory Committee on Drugs and Alcohol study.

This survey found that:

  • 3 in 4 of those surveyed had never used cannabis in their life.
  • 1 in 6 people aged 15-24 had used cannabis in the last year.
  • Younger people were more likely to use cannabis compared to older people.
  • Males use cannabis more often than females.

A second survey took place in 2019, in which children aged 15-16 were surveyed in school. This was part of a larger European study on drug habits called the ESPAD study.

This survey found:

  • 1 in 10 of 15 – 16 year olds in Ireland had used cannabis in the month before the survey.
  • 1 in 20 reported a pattern of ‘high risk’ cannabis use.

Cannabis is a drug that comes from a plant known by the same name. It is a psychoactive drug which means that it affects how our brains work causing changes in thoughts, feelings, mood or/and awareness.

A psychoactive drug such as cannabis or alcohol acts mainly on our brains. It changes brain function, resulting in temporary changes in mood, consciousness, behaviour and perception (how we hear, see and become aware of things).

Cannabis has many slang words (‘weed’, ‘blow’, ‘hash’, ‘dope’, ‘grass’).

Cannabis is most commonly available in Ireland in the form of herbal cannabis –  dried leaves – called ‘weed’ or in a dark sticky substance called resin (‘hash’/’hashish’). Often these types of cannabis are smoked in cigarettes sometimes called a joint or a spliff. Smoking is the most common way to use cannabis.

Cannabis can also be eaten mixed with food. These are called ‘edibles’. Cannabis is sometimes baked into cakes like brownies. More recently, cannabis products are made in the form of sweets. These can appear in the form of jellies like ‘gummy bears’ or like chocolate. They can come in colourful plastic wrapping that makes them look like sweets bought in a sweet shop. One of the risks of this form is that young children, or even pets, mistake these cannabis products for sweets leading to accidental poisonings.

Cannabis can also be taken in other ways such as inhaling it by vaping or ‘dabbing’. There are also high potency cannabis extracts, such as oil, shatter or wax.

Cannabis contains chemicals that affect the body and the mind. These chemicals are called cannabinoids.

For most people, the effects from using cannabis wear off after a couple of hours.

Many users report pleasurable effects, including a feeling of relaxation and mild euphoria (well-being).  Some people describe being ‘high’ or ‘stoned’ and feeling relaxed and/or happy.

However, many people can also feel more anxious, afraid or worried when they use cannabis. Some get panic attacks. Sometimes people become paranoid and very suspicious of other people. They feel others are talking about them and get very stressed. Sometimes people also feel physically sick and have to throw up after using cannabis.

Cannabinoids are the naturally occurring compounds found inside the cannabis plant that have effects on the body or mind. There are over a hundred different cannabinoids in the cannabis plant, but the two that are most well-known are THC and CBD.

THC is the short name for delta-9-tetrahydrocannabinol, and CBD is short for cannabidiol.

Cannabinoids affect our body mainly by interacting with a system called the endocannabinoid system. The endocannabinoid system controls our memory, mood, sleep, appetite and fertility.

Many man-made cannabinoids also exist and are designed to imitate the actions of THC with a higher risk of negative and dangerous effects on our bodies.

The two cannabinoids act quite differently.


THC is the psychoactive substance in the cannabis plant that gives you a ‘high’. It can make you feel happy or giddy but also suspicious and paranoid. It can make you anxious. THC can lead to dependence. Dependence, sometimes called ‘addiction’, means your body gets used to cannabis, and you might feel bad if you don’t have it.

THC can cause:

  • hallucinations (where someone sees, hears, smells, tastes or feels things that don’t exist outside their mind).
  • paranoid thoughts (feelings of anxiety, feeling threatened or persecuted).
  • agitation (anxiety or nervous excitement).

It can also reduce our thinking power and affect our short-term and long-term memory. It affects how we process and keep information in our brain.


CBD does not appear to have intoxicating effects. For more information, see our separate webpage and information sheet on CBD.

THC content in cannabis today is much higher than in the past, and its strength varies from batch to batch. Samples of cannabis seized by the Irish authorities and tested have found that the amount of THC ranges from 1 – 16%.

In the 1960s, cannabis had just 1 – 2 % THC but in recent years it has up to 20% THC with stronger strains available in America and Europe. Cannabis with a THC content of over 10% is called high-potency cannabis.

Cannabis products designed to eaten, called ‘edibles’, can have even higher levels of THC.

Cannabis that is eaten takes longer to take effect compared to cannabis that is smoked. This can lead to people taking more cannabis than they initially intended. This can lead to people having bad experiences and possibly even requiring hospital treatment.

The cannabis products used in vaping and ‘dabbing’ also contain more THC than in the typical cannabis herbal joint.

The THC level matters a lot as cannabis with high levels of THC is more harmful.

Studies show that the higher the THC content, the greater the risk of becoming psychotic, agitated or anxious.

Section 2: The general risks of cannabis

Cannabis smoke contains many toxic substances and poisons found in tobacco smoke (for example, carbon monoxide, aldehydes, acrolein, phenols and carcinogenic polycyclic aromatic hydrocarbons).

The number of admissions to general hospitals (in Ireland) of young adults with a cannabis-related diagnosis trebled between 2005 and 2017.

The physical dangers of cannabis include:


Cannabis use can cause a form of repeated vomiting. This is called Cannabis Hyperemesis Syndrome which often needs to be treated in hospital because you can become dehydrated and lose salt from your body. This can be very serious when vomiting is severe.

Heart and breathing problems

Cannabis use also causes problems for people with breathing problems as well as heart problems.


Cannabis use can also increase the rates of certain types of cancer.

Reduced life expectancy

People who have a Cannabis Use Disorder have reduced life expectancy. The reasons for this are not fully understood.

Yes. Cannabis is addictive and can lead to what is called Cannabis Use Disorder. This means a person has a problem with their cannabis use and is no longer in control of it. People who use cannabis for a long time and then give up often have problems with their mood, temper and sleep. There can be significant withdrawal effects such as irritability, anxiety, decreased appetite, restlessness, and sleep disturbance.

Studies show that 1 in 5 adults who use cannabis are likely to have a cannabis dependence. The risks in young people are even higher with 1 in 3 young people likely to become addicted if they use weekly or more often.

A Cannabis Use Disorder is the most common reason young people under the age of 25 years look for addiction treatment. It is even more common than alcohol or other drugs like heroin or cocaine. The number of teenagers (aged 13-17) entering the addiction treatment service (specialist services) doubled between the year 2006 and 2016. This was based on data from National Drug Treatment Reporting System (NDTRS).

Studies found three main causes for young people developing a Cannabis Use Disorder.

  • using cannabis from a very young age (a US study showed that people who begin using cannabis before they are 18 are four to seven times more likely to develop this disorder).
  • using a lot of cannabis on a regular basis.
  • using cannabis with a high THC level (THC is the mood-altering chemical in cannabis).

Sometimes people start using cannabis and afterwards go on to using different drugs like heroin, cocaine or amphetamine. In this way, cannabis can act as a gateway (stepping stone) to using other drugs. Not everyone who uses cannabis goes on to using other drugs. Cannabis can make people more likely to make risky decisions and this might be one way this happens.

People who use cannabis every day or almost every day are likely to experience mental health problems.

People who use cannabis less often are still more likely than those who have never used cannabis to experience a mental health problem.

One study found  that exposure to a small amount of cannabis in early adolescence may be related to changes in the structure of the brain.

Cannabis use makes it more difficult to drive a car or other vehicle safely. This is because cannabis delays your reaction times and decision-making skills. This impairs a person’s ability to drive or operate machinery.

When cannabis and alcohol are taken at the same time this makes a person’s driving or operating of machinery even more dangerous. A recent study suggests that long-term cannabis use can impair users’ driving even after a 12-hour abstinence period.

The Gardaí can test people at the roadside for cannabis and can arrest people found to be under the influence of cannabis when driving.

In 2018, cannabis was implicated in 1,205 cases of road traffic offences according to the Medical Bureau of Road Safety.

There has been an increase in road traffic accidents in some places where cannabis has been legalised.

Yes. It can.

Cannabis use is not only associated with harms for the user. It also affects the user’s family and the community they live in.

This is most likely to happen if a person develops a Cannabis Use Disorder or cannabis dependence (see question 9).

Can cause family problems

Many parents say that their young person’s Cannabis Use Disorder caused many problems for the family including aggressive behaviour at home, stealing from family and money problems.

If a parent has a Cannabis Use Disorder, this can make it harder for them to parent their children.

May cause more traffic accidents

Cannabis use has also been connected to many road traffic accidents. When a person is under the influence of cannabis, their concentration is affected. They are more likely to have an accident (than when they are not under the influence of cannabis).

May cause violence

Like alcohol and other drug problems, a Cannabis Use Disorder can increase the risk of violent behaviour, especially in people with psychotic illness.

Using cannabis while pregnant is associated with low birth weight and disruption to the growth of the baby’s brain, which may lead to neurodevelopmental problems (including autism spectrum disorder). For these reasons, it is best to avoid taking cannabis while pregnant. If a woman stops using cannabis after finding out she is pregnant, the risks can be reduced a lot. Supporting pregnant women who use cannabis to get help is very important.

Section 3. Cannabis and mental health

Yes. Cannabis can make existing mental illness get worse. Cannabis use can trigger new mental illness, that is, sometimes people become mentally ill for the first time very soon after using cannabis. The number of people admitted to psychiatric hospitals in Ireland with a cannabis related diagnosis has trebled since 2002.


Cannabis is linked with psychosis. Psychosis is a condition in which a person’s thoughts and perceptions are disturbed, and they have difficulty understanding what is real and what is not. Sometimes they hear voices in their head or have strong false beliefs. Cannabis users are three to four times more likely to develop psychosis than those who never use it.


Cannabis can make depression worse. It can also bring on depression. It is more likely if the person regularly takes high-potency cannabis (with high amounts of THC- the mood changing chemical).

The younger a person begins using cannabis, the more at risk they are of developing a Major Depressive Disorder. Cannabis Use Disorder has been associated with a greater risk of developing Bipolar Affective Disorder and having more frequent relapses.

Anxiety Disorders

Cannabis can make Anxiety Disorders worse. Adolescent cannabis users are at higher risk of developing Anxiety Disorders, particularly those people who use high-potency cannabis (with high amounts of THC- the mood changing chemical).

Self-harm and suicidal behaviour

Cannabis use is also associated with self-harm and suicidal behaviour. Young people who smoke cannabis regularly are three times more likely to attempt suicide than people who never use cannabis.

Long-term cannabis users are more likely to report thoughts of suicide than non-users. In 2018, cannabis was the most common street drug used among men aged 15 – 24 who had self-harmed in Ireland.

Right now, there is no research to support the use of cannabis to treat mental illness. Currently, there are no cannabis based products which can be recommended in the treatment of any type of mental illness in Ireland.

People living with mental illnesses may self-medicate with cannabis instead of speaking to their doctor. This means that they delay seeking professional help, and getting proven effective treatments.

Just like other drugs, including alcohol, many people experience pleasurable short-term effects of cannabis use. Overall, the longer term effects appear negative. You need to know the risks involved with cannabis use, so that you can make an informed decision about it.

Unfortunately, research suggests that, in recent years, knowledge of the harms of cannabis amongst people – particularly young people – has decreased.

Factors contributing to this include:

  • positive media coverage of cannabis use
  • social media misinformation
  • positive marketing of cannabis based products by companies
  • confusion about ‘medicinal’ uses and benefits to health of cannabis based products

Chronic psychosis is a serious and long-term mental illness that can cause disability. The chances of cannabis users developing chronic psychosis are higher if:

  • the cannabis contains high levels of the ingredient THC (mind-altering chemical)
  • this high-potency cannabis is used regularly
  • use starts at a younger age

There are other factors that contribute to the risk of a person developing long-term psychosis. Children with parents or other family members who have psychotic illnesses, like schizophrenia, are at higher risk. Growing up in a stressful environment is also a risk.

The evidence shows that heavy use of strong cannabis at an early age is a big risk factor for developing long-term psychosis. However, some people use small amounts of cannabis on rare occasions and still develop a long-term psychosis.

Cannabis effects areas of the brain that are still being developed.

Using cannabis is linked to having a different brain structure and different brain development, particularly in people under 25. Young people’s brains don’t stop growing and changing until well after the age of 25.

While regular and long-term use of cannabis is associated with differences in brain structures, one recent study has shown that even low exposure to cannabis as a teenager may change the brain.

Using cannabis can have negative effects on how you get on in school, college and work. Many studies in different countries have shown that young people who use cannabis do worse in school exams and job applications than young people that don’t use it.

Using high strength cannabis regularly harms parts of what makes you intelligent – like your memory, and your ability to learn and make good decisions. For most young people this can go back to normal when you stop using.

Many studies have shown that using cannabis in the early stages of life is strongly linked to:

  • lower levels of education and income
  • unemployment
  • greater need for social welfare benefits
  • lower satisfaction in life
  • relationship problems

For more information and support

Contact the HSE Drugs and Alcohol Helpline for free and confidential support and information:

Phone: 1800 459 459


Visit: (Policy Information: Drugs and Alcohol Policy)


References for all the information in this document can be found here.