Rehab 4 Addiction

Cannabis has been the subject of many investigations over the years as medical researchers seek to understand the effects that consuming cannabis can have on a person’s brain chemistry, emotional state and behaviour.

There has been plenty of research into the link between cannabis use and the psychosis associated with schizophrenia, and also, the effect it can have on a person’s mental health.

There are many factors to be considered when assessing whether cannabis use directly causes poor mental health, anxiety and aggressive tendencies.

What is clear is that there are chemical properties in cannabis that do negatively affect our brain biology, the result of which can adversely alter our behaviour.


Cannabis is a psychoactive drug that is derived from the Cannabis Sativa plant, it is the second most-consumed drug in the UK after alcohol and is a popular drug with teenagers as they begin to experiment with substances to experience their pleasurable effects.

Cannabis was recognised for its medicinal qualities centuries ago and although many people used the drug for its therapeutic effects, it has now come to be regularly sought after for the calming effect it has on the human body, and for the pleasurable feelings, it produces. (3,4)

Cannabis usually comes in 3 forms in the UK, these being cannabis resin, sinsemilla (including skunk) and marijuana.

Each of these three varieties tends to be different in the balance of chemicals that they contain.

For example, the main psychoactive ingredient in all forms of cannabis is THC, and there is more THC in the skunk form of cannabis than in the cannabis resin form. (2)

Chemical content of cannabis

Cannabis contains over 500 different chemicals with THC being the main psychoactive component that is chiefly responsible for generating the feelings of pleasure and relaxation that people experience when they consume the drug.

However, research has yet to uncover the effects that the majority of these chemicals have on the functioning of the human brain and subsequent behaviour. (4,9)

It is thought there are between 50-60 chemicals that may be able to produce similar effects to THC but no research has been able to identify the exact chemical make-up of any of these elements let alone state with any certainty the effect they have on the human brain. (9)

Cannabis is a psychoactive drug

If a drug is psychoactive, it means that it contains chemicals that can have a significant effect on our brain chemistry and change the way we perceive the world, and therefore the way we behave.

The chemicals in cannabis can attach to receptors in the brain and activate areas that govern certain aspects of our behaviour.

For example, most psychoactive drugs trigger the reward pathway in the brain that is responsible for controlling our emotional experiences, which is why people who consume cannabis experience feelings of pleasure and relaxation.

Unfortunately, prolonged use of cannabis can lead to other changes in our brain chemistry that tend to have negative consequences for us.

Cannabis causes a decline in cognitive performance

There have been many reported cognitive deficiencies associated with cannabis use, for example, problems with memory recall, poor impulse control, a decline in our ability to pay attention and concentrate, and a significant reduction in our problem-solving abilities.

Users may also have problems with coordination, and reaction time as well as become prone to engaging in fantasies.

The decline in these cognitive abilities can lead to many changes in a person’s behaviour and, in their interactions with others.

A reduction in these abilities can affect our day to day functioning as we may find it hard to keep track of conversations both socially and professionally and show enough cognitive competence to carry out our work and family commitments. (1,8)

Endocannabinoid System

Some of the chemicals found in cannabis have been reported to connect to the receptors in the Endocannabinoid system in the human brain, an area that is responsible for controlling several aspects of our emotional behaviour.

Anger is of course a strong emotion so any psychoactive drug that can act upon the cannabinoid receptors in our brains can have a huge influence on our general mood and emotional life, including our responses to people, and events that feature in our environment.

Cannabis changes our conscious experience

Consuming cannabis has been shown to remove the user from being preoccupied with day-to-day concerns.

Certain chemicals in cannabis can change the way a person experiences reality and affects the way they perceive the environment (including people) around them. (2)

This makes them more unpredictable and more likely to display erratic behaviour.

There are many negative consequences of taking cannabis and it has been well documented that cannabis affects us in certain ways that can make us more likely to become violent. (4,9)

Cannabis induces psychosis

It has been suggested that the chemicals in cannabis have the potential to transform the way people perceive events in their environment, this can lead to the development of psychosis which has long been established as a consequence of excessive cannabis consumption. (2,3)

Once in this state, the behaviour of a person becomes unpredictable with the potential for misunderstandings and a huge tendency to misinterpret events that occur.

When coupled with paranoia there is a strong chance that this will lead to aggressive or/and violent behaviour.

People who develop psychosis tend to lose touch with the reality going on around them, they may have delusions and false beliefs about themselves and other people, and this may lead to them behaving inappropriately in social situations as cannabis has decreased their ability to make accurate social judgements. (2,3)

Scenarios like this increase the risk of aggressive and violent encounters as cannabis has altered many aspects of their cognition.

The significance of THC

It has been claimed that the THC component in cannabis impairs the ability of people to perceive their surrounding environment accurately which can lead to paranoia and anxiety and when these two states combine people can behave erratically which can make them more predisposed to aggressive and violent behaviour. (4,6)

Cannabis and panic attacks

It has been found in experimental studies that cannabis consumption leads to panic attacks, confusion, hallucinations, paranoia and suspiciousness, these cognitive changes increase the likelihood that people who take cannabis will react aggressively to any perceived threats, injustices or provocations from others. (1,4)


Consuming cannabis tends to instigate a lot of changes in our internal biology which can affect our behaviour, this is because the chemicals in cannabis interfere with several parts of our brain that usually perform vital functions for us. (9)

Research has strongly indicated that consuming cannabis does elicit negative personality changes in people, such as making them more suspicious (paranoid), fearful, angry and aggressive.

A state of paranoia has been consistently associated with violent and aggressive behaviour. (4,5,6)

When you consider that cannabis also increases heart rate and arousal levels which prepare people for physical activity then it is no surprise to learn that this may lead to aggression and violence.

Cannabis use affects our self-control

There have been medical studies conducted that suggest that even a single dose of cannabis can lead to people losing the ability to control their behaviour.

They might be vulnerable to impulsive behaviour and be unable to control their emotional responses in social situations.

This means they are more likely to become aggressive and physically violent as cannabis has impaired their ability to regulate their emotional behaviour.

The area of our brain that governs our ability to show restraint has been altered by the chemicals in cannabis. (4,6)

Cannabis Withdrawal symptoms and aggression

Regular users of cannabis may find that they experience a range of withdrawal symptoms when they stop taking the drug for a while or attempt to give up. These symptoms include disrupted sleep, restlessness, irritability and anxiety. (3,9)

These symptoms can make a person prone to having an angry demeanour and behaving aggressively.

Research findings have reported that withdrawing from cannabis can lead to people bullying others and acting violently, even towards themselves which increases the risk of self-harm. This is particularly the case for heavy cannabis users with a predisposition to aggressive behaviour. (4,6)

If a person has reached the point where they need to consume cannabis to satisfy withdrawal symptoms, then they may well display an agitated state and be more prone to acting aggressively. (4,6)


When brought together, the combination of poor judgement and decision making, paranoia, changes in perception, increased heart rate and poor emotional control it is easy to see how excessive cannabis use will increase the likelihood of a person becoming angry and aggressive.


(1) Castle, D., Murray, R.M., D’Souza, D. (2012) Marijuana and Madness. Cambridge University Press. Cambridge.

(2) Hughes, L. (2010) Cannabis Use and Psychosis. In Phillips, P., McKeown, O. Sandford, T. Dual Diagnosis: Practice in Context. Wiley-Blackwell. Chichester.

(3) Kahan, M. (2014) Physical Effects of Alcohol and Other Drugs. In Herie, M. & Skinner, W. (ed) Fundamentals of Addiction: A Practical Guide for Counsellors. CAMH. Canada.

(4) Miller, N., Ipeku, R., Oberbarnscheidt, T, (2020) A Review of cases of marijuana and violence. Available @A Review of Cases of Marijuana and Violence (

(4) Moss, A, Dyer, K (2010) The Psychology of Addictive Behaviour. Palgrave McMillan. New York.

(5) Royal College of Psychiatrists (2022) How does cannabis affect mental health. available@ Cannabis and mental health – for young people | Royal College of Psychiatrists (

(6) Schoeler, T, et al (2016) Continuity of cannabis use and violent offending over the life course. Available @Continuity of cannabis use and violent offending over the life course – PubMed (

(8) Solowij, N. (1998) Cannabis, and Cognitive Functioning. Cambridge University Press. Cambridge.

(9) Stoner, S. (2017) Effects of marijuana on mental health. Alcohol and drug abuse institute, University of Washington. Available @ 2017mjdepression.pdf (




Boris is our editor-in-chief at Rehab 4 Addiction. Boris is an addiction expert with more than 20 years in the field.  His expertise covers a broad of topics relating to addiction, rehab and recovery. Boris is an addiction therapist and assists in the alcohol detox and rehab process. Boris has been featured on a variety of websites, including the BBC, Verywell Mind and Healthline.