Professional Reference articles are designed for health professionals to use. They are written by UK doctors and based on research evidence, UK and European Guidelines. You may find the Recreational Drugs article more useful, or one of our other health articles.
Treatment of almost all medical conditions has been affected by the COVID-19 pandemic. NICE has issued rapid update guidelines in relation to many of these. This guidance is changing frequently. Please visit https://www.nice.org.uk/covid-19 to see if there is temporary guidance issued by NICE in relation to the management of this condition, which may vary from the information given below.
Synonyms (street names): hash, hashish, weed, pot, marijuana, ganja, dope, skunk, grass, puff
What is cannabis?
Cannabis is the collective term for a range of psychoactive preparations of the cannabis plant, Cannabis sativa, and related species and hybrids. Cannabis contains cannabinoids, a class of diverse chemical compounds that act on endogenous cannabinoid receptors that modulate neurotransmitter release in the brain. The principal psychoactive cannabinoid is δ-9-tetrahydrocannabinol (THC).
Cannabis is typically smoked in the form of the flowering heads or leaves of the marijuana plant. Tobacco is often mixed with cannabis when smoked. Cannabis extracts may also be vaped or eaten.
There are also cannabis oils that are prepared from these same sources. These preparations vary considerably in their THC potency. Hash (hashish) is a cannabis concentrate product composed of compressed or purified preparations of stalked resin glands from the plant, consumed by smoking, typically in a pipe.
Cannabis has predominantly central nervous system depressant effects and produces a characteristic euphoria that may be part of the presenting features of cannabis intoxication, which may also include impairment in cognitive and psychomotor functioning.
Cannabis has dependence-producing properties resulting in dependence in some people and withdrawal symptoms when use is reduced or discontinued.
Cannabis was reclassified from a class C to class B drug in January 2009.
How common is cannabis use? (Epidemiology)
Since estimates began in the year ending December 1995, cannabis has consistently been the most used illegal drug in England and Wales.
In the year ending June 2022, 7.4% and 16.2% of adults aged 16 to 59 years and 16 to 24 years, respectively, reported having used the drug in the previous year, which is a similar level to the year ending March 2020 and the year ending March 2012; however, levels are much lower compared with the year ending December 1995.
Cannabis induces a relaxed state characterised by a series of disconnected thoughts. There may also be:
- Alteration in perception of time, colour and space.
- Short-term memory loss.
- Dry mouth.
- Dry eyes.
- Bloodshot eyes.
- Increased heart rate.
Effects are prolonged for 2-3 hours after smoking, with no clear evidence of hangover or lasting effect.
Ability to drive and ability to operate machinery are impaired due to effects on motor skills and depth perception.
Symptoms of schizophrenia may be worsened.
Cannabis withdrawal causes a cluster of symptoms, behaviours and/or physiological features, varying in degree of severity and duration, affecting people who have developed cannabis dependence or have used cannabis for a prolonged period or in large amounts.
Presenting features of cannabis withdrawal may include irritability, anger or aggressive behaviour, shakiness, insomnia, restlessness, anxiety, depressed or dysphoric mood, decreased appetite and weight loss, headache, sweating or chills, abdominal cramps and muscle aches.
The onset of cannabis withdrawal typically occurs at some point between 12 hours and 3 days after cessation or reduction of use. Symptom severity typically peaks at 4 to 7 days and may last for 1 to 3 weeks after cessation of use. However, cannabis withdrawal may also be briefer, in some cases lasting only a few days.
When cannabis withdrawal occurs in the context of a co-occurring mental disorder, the features of the other disorder (eg, fluctuation of mood) may be exacerbated.
Cannabis withdrawal symptoms become more severe with repeated episodes of withdrawal, with aging, or in the presence of comorbid medical conditions.
A significant subpopulation of frequent cannabis or THC users will develop a drug use syndrome termed cannabis use disorder. Individuals suffering from cannabis use disorder exhibit many of the hallmarks of classical addictions including cravings, tolerance, and withdrawal symptoms.
Using cannabis causes a number of physical effects including increased pulse rate, decreased blood pressure, bloodshot eyes, increased appetite, tiredness and occasionally, dizziness. These effects can start within a few minutes and may last several hours depending on how much is taken.
While the effects of use rely on dose and the expectations and mood of the user, cannabis can often lead to a state of relaxation, talkativeness and the giggles. There is also a greater appreciation of sensory experiences such as music, and hallucinations may occur with higher doses. It can be taken to enhance or detract from the effects of other drugs such as ecstasy or cocaine, particularly after long dance sessions.
While intoxicated, cannabis can affect short-term memory, concentration, and intellectual or manual dexterity, including driving. Higher doses can lead to perceptual distortion, forgetfulness and confusion of thought processes. Temporary psychological distress and confusion can occur, particularly among inexperienced users or if the user is feeling anxious or depressed.
The physical effects of inhaling and smoking cannabis can impact on the respiratory system, leading to an increased risk of oral, throat, and lung cancer.
Some studies suggest an association with spontaneous pneumothorax. It is also linked to bullous emphysema and COPD complications, such as increased wheezing, cough, and phlegm production.
Long-term use has also been associated with periodontal disease, impaired spermatogenesis, pre-term birth if used at 20 weeks gestation, and more frequent pain crises in sickle cell patients.
Chronic use has also been well documented as a cause of cannabinoid hyperemesis syndrome, which causes recurrent episodes of nausea and vomiting that are relieved by hot showers.
The use of cannabis has been reported to cause panic attacks, anxiety and paranoia in some users and studies have suggested that it can be a trigger for underlying mental health problems.
Mental health disorders
Cannabis is associated with a range of mental health disorders. In a national stratified Australian sample of persons aged 18 years and older, 7 in 10 persons with cannabis addiction had another psychiatric disorder, compared with 1.5 in 10 individuals who did not use cannabis.
Similarly, in US surveys, the presence of cannabis addiction in the past 12 months was significantly associated with a high risk of any mood disorder, anxiety disorder, post-traumatic stress disorder (PTSD) and personality disorder.
A meta-analysis of epidemiological and clinical studies predominantly in the USA and Europe found that 12% of people who had been treated for, or diagnosed with, major depressive disorder had cannabis addiction.
In clinical and population studies:
- 24% of people with bipolar disorder use cannabis and 20% have cannabis addiction.
- 26.6% of patients with schizophrenia have current or previous cannabis addiction. The prevalence varies substantially by region with the highest prevalence in the UK (36.7%), followed by Australia (35.2%), Europe (27.8%), North America (23.5%) and all other regions (4.5%).
- Data on the comorbidity of cannabis addiction with other psychiatric disorders are less consistent.
The use of cannabis, particularly high potency cannabis, has been associated with cases of first onset psychosis.
However, the link between cannabis and mental health disorders is not certain. Although cannabis has been linked with anxiety, anxiety is also a trigger for cannabis use, and a large meta-analysis did not find a convincing link between cannabis and anxiety. This was reiterated in a recent epidemiological study that did not find such a correlation, but did identify a link between cannabis use, substance disorder, alcohol use disorder, drug use disorder, and nicotine dependence. Similarly, contradicting data exists regarding the link of depression and cannabis use.
Management of cannabis dependence
The optimal treatments for most substance use disorders combine psychosocial and pharmacological interventions.
No effective pharmacological approaches for CUD are available. Psychosocial-based interventions, including cognitive behavioural therapy (CBT), motivational enhancement therapy (MET) and abstinence-based contingency management combined with CBT and MET, are, therefore, the first-line treatment for adolescents and adults.
There is mixed support for prevention approaches such as media campaigns, and school-based, family-based and community-based programmes.
Use of cannabis in medical treatment
See the article on Cannabis-based Medicinal Products.
Further reading and references
Fischer B, Lindner SR, Hall W; Cannabis use and public health: time for a comprehensive harm-to-others framework. Lancet Public Health. 2022 Oct7(10):e808-e809. doi: 10.1016/S2468-2667(22)00205-5.
Volkow ND, Swanson JM, Evins AE, et al; Effects of Cannabis Use on Human Behavior, Including Cognition, Motivation, and Psychosis: A Review. JAMA Psychiatry. 2016 Mar73(3):292-7. doi: 10.1001/jamapsychiatry.2015.3278.
Thomasius R, Paschke K, Arnaud N; Substance-Use Disorders in Children and Adolescents. Dtsch Arztebl Int. 2022 Jun 24119(25):440-450. doi: 10.3238/arztebl.m2022.0122.
Brezing CA, Levin FR; The Current State of Pharmacological Treatments for Cannabis Use Disorder and Withdrawal. Neuropsychopharmacology. 2018 Jan43(1):173-194. doi: 10.1038/npp.2017.212. Epub 2017 Sep 6.
International Classification of Diseases 11th Revision; World Health Organization, 2019/2021
Drug misuse in England and Wales: year ending June 2022; Office for National Statistics (ONS).
Saugy M, Avois L, Saudan C, et al; Cannabis and sport. Br J Sports Med. 2006 Jul40 Suppl 1:i13-5.
Sharma P, Murthy P, Bharath MM; Chemistry, metabolism, and toxicology of cannabis: clinical implications. Iran J Psychiatry. 2012 Fall7(4):149-56.
Turner AR, Agrawal S; Marijuana. StatPearls, Aug 2022.
Kesner AJ, Lovinger DM; Cannabis use, abuse, and withdrawal: Cannabinergic mechanisms, clinical, and preclinical findings. J Neurochem. 2021 Jun157(5):1674-1696. doi: 10.1111/jnc.15369. Epub 2021 May 16.
Connor JP, Stjepanovic D, Le Foll B, et al; Cannabis use and cannabis use disorder. Nat Rev Dis Primers. 2021 Feb 257(1):16. doi: 10.1038/s41572-021-00247-4.
Di Forti M, Marconi A, Carra E, et al; Proportion of patients in south London with first-episode psychosis attributable to use of high potency cannabis: a case-control study. Lancet Psychiatry. 2015 Mar2(3):233-8. doi: 10.1016/S2215-0366(14)00117-5. Epub 2015 Feb 25.
Urits I, Gress K, Charipova K, et al; Cannabis Use and its Association with Psychological Disorders. Psychopharmacol Bull. 2020 May 1950(2):56-67.