On rare occasions, cannabis use can induce a state of psychosis in individuals with a genetic predisposition. As a result, patients with a (family) history of psychotic disorders, particularly schizophrenia and bipolar disorder, should be under careful psychiatric monitoring when using medicinal cannabis. Moreover, a short, acute psychotic like episode (involving anxiety and catastrophic thinking) is possible in the case of non-predisposed individuals, especially when very high doses of THC is taken.
Occasionally, new scientific reports appear on the effects of cannabis on risk of psychosis. However, a direct link between cannabis and psychosis has not yet been established. The discourse surrounds the question: does cannabis induce psychosis in otherwise totally healthy individuals, or does pre-existing genetic vulnerability for psychosis result in adverse outcomes from cannabis use?
Recent scientific studies into this matter suggest a small proportion of the population has genetic predispositions that increase the risk of developing chronic psychotic symptoms when using cannabis (as a medicine or otherwise).
Cannabinoids can have a strong, but temporary, effect on heart rate and blood pressure. Patients with a history of heart disease or receiving medication for heart disease should avoid their use, or only use cannabis under careful supervision by a medical doctor.
Pregnancy and lactation
The use of cannabis during pregnancy is likely to affect the development of the fetus. Because certain cannabinoids – including THC – are excreted in breast milk, the use of medicinal cannabis is also not advised while breastfeeding.
After cannabis administration, the liver is the main organ involved in chemically altering the cannabinoids as part of its function to process and excrete external substances by the body (metabolism). The effects of cannabis may therefore be significantly different in patients with a liver disease. Therefore, these patients should be monitored during initiation to ensure the dose taken does not exceed the liver’s capacity to metabolise.
The evidence suggests that the risk of developing an addiction to cannabis when taken as a medicine is minimal. The recommended dose for medicinal use is often lower than that of a recreational user, and a medical professional should always be involved in medicating and monitoring the patient.
Patients should take particular care, however, if they have prior problematic substance use. High doses of medicinal cannabis, taken over long periods, may lead to dose escalation and misuse. The abrupt cessation (quitting) may then cause withdrawal symptoms, such as mild forms of restlessness, irritability, insomnia, vivid dreams, and decreased appetite.
The consumption of medicinal cannabis has not been shown to lead to life threatening adverse events, even at very high doses. However, an overdose of cannabis (THC) can result in a range of adverse effects, with high variability in tolerance between subjects. The most common adverse effect of overdosing a single dose of THC is anxiety, which, in some cases, may lead to mild acute psychotic states (panic attacks). In addition, increased heart rate and changes in blood pressure may occur.
Specifically, it is possible that a THC overdose will result in acute hypotension and/or tachycardia. In some cases, nausea and vomiting and diarrhea may be observed as well. That aside, impaired executive function and motor control may lead to feelings of confusion, depersonalisation, loss of control, or even helplessness. Also reddened eyes and a dry mouth may be experienced as very unpleasant to some individuals. Most adverse effects will spontaneously resolve, usually within a few hours, when serum levels of THC fall.
There are suggestions that in a small number of cases THC is capable of precipitating psychosis, involving delusions and hallucinations. If these side effects occur, they seem to be rare, because they most likely require very high doses of THC administered over a prolonged period of time, or a pre-existing genetic vulnerability. However, there is enough reason to be cautious and communicate these risks in a fair and balanced way.
Driving and operating machinery
At therapeutic doses, cannabis may produce undesirable effects such as dizziness and drowsiness which may impair judgement and performance. Patients should not drive, operate machinery or engage in any potentially hazardous activity under the influence of medicinal cannabis or cannabinoid therapeutic products that contain THC.