Rehab 4 Addiction


Despite being an illegal controlled substance, cannabis is one of the most widely used drugs in the UK, and use has been largely destigmatised.

Although cannabis cannot cause an overdose in the same way that heroin or cocaine can, the drug can cause an immense amount of damage in terms of cognitive function and psychological wellbeing.

It is important not to fall for the myth that cannabis is a ‘harmless’ drug. Below we have listed a number of ways in which cannabis can affect the function of the brain.

How THC affects the brain and the body

THC is the main psychoactive component of cannabis, and higher levels of THC will generally produce stronger effects on the user.

Smoking or ingesting cannabis can cause a number of short-term physical and psychological symptoms. We have compiled a brief list below:

  • Lack of coordination – The THC component of cannabis can interfere with the normal function of the cerebellum. This can lead to temporarily hampered motor skills and hand-eye coordination.
  • Slowed reactions – cannabis users are generally slower to respond to verbal cues and other stimuli when under the influence of the drug.
  • Increased heart rate – cannabinoids have a complex effect on the user’s cardiovascular system, making the heart pump harder and raising their resting heart rate.
  • Memory loss – cannabis use is strongly linked with short-term and long-term memory loss. The effect can be documented in both casual users and chronic users.
  • Anxiety – cannabinoids like THC can overstimulate the amygdala, making a person more prone to episodes of anxiety. This is especially true for those who already suffer with anxiety disorders.
  • Paranoia – your amygdala regulates your response to fear and stress, which includes stress, anxiety, and paranoia. As THC affects the amygdala, cannabis can cause paranoid or otherwise problematic thought patterns to develop.

Cannabis effects on adolescents

Cannabis use is widespread among adolescents, more so than most other age groups. This can be very problematic in terms of their psychosocial development.

A recent study revealed that 37 percent of high school students admitted to having used the drug, with 22% of those surveyed saying they had used it within the last month. [1]

Adolescents’ brains are still developing and will continue to do so until around the age of 25. Using cannabis as a teen can lead to a wide range of developmental problems.

Several studies have linked adolescent cannabis use with early-onset psychosis, as well as being increasingly prone to developing depression and anxiety disorders.

Teen cannabis use also affects cognitive development, affecting things like attention levels, decision making, verbal fluency, and impulse control.

How quickly does cannabis take effect?

The short-term effects of cannabis generally manifest within a period of about 2 minutes, when the drug is smoked. If eaten, cannabis can take much longer to take effect – around 45 minutes.

Eating cannabis, for example in a cookie or cake, is always much more unpredictable in terms of measuring dosage and the drug’s effects on the user.

Everyone who uses cannabis will also have a different level of tolerance to the drug, which depends on a number of different physiological and psychological factors.

Levels of THC in cannabis

The psychological and physical side effects of cannabis are dependent on the levels of THC in the strain that they are consuming, among other factors.

The levels of THC in cannabis have increased exponentially over the last 50 years [2], meaning that cannabis bought on the street is likely to be much stronger than in previous years.

This can be a problem for cannabis users, particularly those who are new to the drug and don’t have any idea what their tolerance level is.

This ‘super-strength’ cannabis, particularly the skunk variety, can lead to the unpleasant side effects of cannabis use to be much more intense and harder to manage.

Cannabis and psychosis

Psychosis is a condition where a person has difficulty differentiating what is real and what is not. It can bring about hallucinations, delusions, and erratic and/or violent behaviour.

Psychosis can affect anyone in any walk of life, regardless of their mental health and medical history. However, certain lifestyle factors can make psychosis more likely to develop within a person.

Cannabis has been linked with a higher risk of developing psychosis. Even short-term ‘one-off’ cannabis use increases the risk of a psychotic episode.

Long-term cannabis use also increases the risk of developing a psychotic illness, which includes schizophrenia. [3]

Long-term effects of cannabis on the brain

In the long term, cannabis can inflict a great amount of damage in terms of the person’s physical and mental health, as well as their social life and overall wellbeing.

As well as making a person more prone to mental illness, long-term cannabis abuse is also likely to lead to a marked decline in cognitive function.

In fact, a longitudinal study that was conducted in New Zealand found that regular cannabis use in teen years can lead to a loss of between 6 and 8 IQ points in mid-adulthood. [4]

Cannabis use also often causes users to become more socially withdrawn and isolated, making it much more difficult to manage any mental health problems effectively.

Most of those who smoke cannabis do so by combining it with tobacco. This puts users at increased risk of lung cancer, emphysema, stroke, and heart attack.

Cannabis addiction help

Rehab 4 Addiction offers help to people with an addiction to any illicit substance, including cannabis. We do this by providing rehab referrals, as well as operating as a free information resource.

Cannabis rehab can help you to address your issues around cannabis use, manage your cravings, and put together a plan for a healthy future without cannabis abuse.

If cannabis has taken over your life, it is not too late to do something about it. Call today to speak confidentially with one of our advisory team.

Calls to Rehab 4 Addiction are free from UK landlines and we will not pass on your information to anyone else without your consent.


[1] Centre for Disease Control and Prevention. Marijuana and public health: Teens.

[2] Tom Freeman et al. Changes in delta-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) concentrations in cannabis over time: systematic review and meta-analysis

[3] Carsten Hjorthøj et al. Development Over Time of the Population-Attributable Risk Fraction for Cannabis Use Disorder in Schizophrenia

[4] Louise Arsenault et al. Cannabis use in adolescence and risk for adult psychosis: longitudinal prospective study. BMJ, 2002; 325: 1212-3



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.