The side effects of cannabis

People experience different side effects when taking cannabis. Some people will feel spaced out and relaxed, while others will be chatty and happy. The short-term side effects of taking cannabis can also vary depending on age, sex, mental health and the method of administration. When smoked or vaped, cannabis enters the blood stream much more quickly and the user feels the effects almost instantly. Whereas if cannabis is ingested, the ‘high’ is less immediate and may take several hours to wear off. Despite these variables, the detrimental side effects of cannabis have been recognised for many years.

Short-term side effects of cannabis

The World Health Organisation reports that cannabis impairs the capability to learn, impairing thinking, attention-span, memory and recall. Cannabis is also said to impact psychomotor performance, such as being able to multitask, maintain good hand-to-eye coordination or operate complex machinery (2). This explains the significant increase in the risk of car crashes following acute cannabis use, especially fatal collisions (3).

Episodes of nausea and vomiting
Impaired body movement
Breathing problems
Increased heartrate
Sensitivity to light
Mood swings
Anxiety and panic attacks
Memory loss
Visual disturbances
Hallucinations and delusions
Psychotic symptoms

Long-term side effects of cannabis

Scientists are still investigating the long-term side effects of cannabis on the brain. Experts know that teens and young people are particularly susceptible to the harmful effects of Tetrahydrocannabinol (THC) but are yet to determine if the damage caused to the parts of the brain that control attention, memory and learning are permanent (4). The side effects of cannabis on the brain are dependent on many factors including its potency, frequency of use, age of first use and whether or not other substances are involved.

Many people use cannabis regularly, either recreationally or medicinally. Despite cannabis not being as addictive as drugs such as heroin and cocaine, cannabis use disorders affect roughly 10% of the 193 million users in the world (5). As well as the potential for cannabis addiction, People who take cannabis frequently over many years may develop mood disorders and mental health problems. Cannabis can also exacerbate psychotic disorders, making symptoms more severe for sufferers of conditions such as schizophrenia.

Poor cognitive functioning
Inability to perform daily tasks
Cannabis dependence syndrome
Cardiovascular and respiratory diseases
Blocked airways and lung inflammation (if smoked)
Chronic bronchitis (if smoked)
Low birth weight (in pregnant individuals)
Cannabis withdrawal syndrome

Source of information

1. Karila L, Roux P, Rolland B, Benyamina A, Reynaud M, Aubin HJ, Lançon C. Acute and long-term effects of cannabis use: a review. Curr Pharm Des. 2014;20(25):4112-8. doi: 10.2174/13816128113199990620. PMID: 24001294.
2. World Health Organization
3. Preuss Ulrich W., Huestis Marilyn A., Schneider Miriam, Hermann Derik, Lutz Beat, Hasan Alkomiet, Kambeitz Joseph, Wong Jessica W. M., Hoch Eva. Cannabis Use and Car Crashes: A Review. Frontiers in Psychiatry. Vol 12.2021. DOI=10.3389/fpsyt.2021.643315.
4. Meier MH, Caspi A, Ambler A, et al. Persistent cannabis users show neuropsychological decline from childhood to midlife. Proceedings of the National Academy of Sciences. 2012;109(40):E2657-E2664.
5. Connor J, Stjepanovic D, Le Foll B, Hoch E, Budney A, Hall W. Cannabis use and cannabis use disorder. Nature Rev Disease Primers. 2021;7(16). doi:10.1038/s41572-021-00247-4.