31st January 2024

Cannabis

Background

Cannabis is one of the most ingested illicit substances worldwide, and dependence is relatively common. This section will not cover any of the medicinal uses of cannabis.

Tetrahydrocannabinol (THC) is a cannabinoid compound within cannabis that binds to cannabinoid receptors, modulating inhibition of various neurotransmitters, which in turn influences mood, appetite, etc. It is normally released when cannabis is smoked and distributed throughout the body via perfusion with rapid effect on the neural transmitters described above. When ingested orally, distribution is slower, and peak concentrations are reached later. It is a lipophilic compound and, therefore, can accumulate in the body for a long period of time.

Presentation 

Features of acute intoxication include anxiety, increased appetite/cravings, dry mouth and impaired cognitive and psychomotor functioning. Some may also experience rarer effects, such as hallucinations, delusional thoughts and acute psychosis. Withdrawal and/or chronic use can result in lethargy, low mood, agitation, loss of interest and motivation and poor concentration/memory. These symptoms can profoundly impact the life of the person affected, making it difficult to maintain relationships, keep employment and engage in formal education. It is important to remember that independent mood disorders can exist alongside cannabis misuse, and symptoms must be carefully evaluated before any diagnosis is made.

Diagnosis

A careful history will need to be taken, identifying if any cannabis-containing products were ingested, if a similar presentation has been noted before and if any other substances have also been taken. As with many other substance misuse presentations, diagnosis is largely clinical but also relies on collateral information and history gained from the patient if possible. Cannabis can also be tested for in urine – occasional use can be detected for 1-3 weeks, but chronic use can be detected for up to 12 weeks.

Differential diagnosis

Psychosis that can occur with heavy cannabis use could mimic some of the signs and symptoms of schizophrenia,  but the apathy and lethargy that can follow prolonged use could also present similarly to depression.

Management 

Treatment options are largely supportive in nature, with the aim of improving function and mood. If able, sobriety will be encouraged, although a gradual tapering of cannabis use may be favoured to try and avoid withdrawal symptoms. In acute intoxication, symptomatic treatment can be offered as needed, e.g., ensuring a quiet, calm space is available; however, the intoxication usually resolves without any formal intervention.

Psychological therapies can be offered both to support recovery and rehabilitation and, if needed, address any co-occurring/underlying mental health conditions, such as depression, which can become more apparent with abstinence.

References 

• Stringer S, Church L, Keynejad R, Hurn J. Psychiatry P.R.N.: Principles, reality, next steps. Oxford: Oxford University Press; 2020.
• Patel, J. and Marwaha, R. (2022) Cannabis use disorder, National Center for Biotechnology Information. U.S. National Library of Medicine. Available at: https://pubmed.ncbi.nlm.nih.gov/30844158/ (Accessed: December 27, 2022).
• Clinical Guidelines on Drug Misuse and Dependence Update 2017 Independent Expert Working Group. Drug misuse and dependence: UK guidelines on clinical management. UK: Department of Health; 2017.