Evid Based Nurs 12:16 doi:10.1136/ebn.12.1.16
  • Treatment

Review: short-term medical use of cannabis increases risk of non-serious adverse effects

M A Ware

Dr M A Ware, Montreal General Hospital, Montreal, Quebec, Canada; mark.ware{at}


Is medical use of cannabis associated with an increased risk of adverse effects?


Studies selected reported adverse events associated with medical use of cannabis for pain or chemotherapy-induced nausea in patients with chronic diseases such as multiple sclerosis, neuropathic pain, or cancer. Outcomes were serious and non-serious adverse events.


Ovid Medline, PsycINFO, and EMBASE/Excerpta Medica (to Oct 2007), and reference lists were searched for randomised controlled trials (RCTs), observational studies, and case reports. 23 RCTs (n = 2087) and 8 observational studies met the selection criteria. An oral cannabinoid product was used in 15 RCTs, and an oromucosal cannabinoid spray was used in 8 RCTs. Median duration of use was 2 weeks (range 8 h to 12 mo). No trial on medical use of cannabis by smoking reported adverse events.


Meta-analysis of 23 RCTs showed that medical use of cannabis increased the risk of non-serious, but not serious, adverse events (table).

Adverse events with medical use of cannabis v control in 23 randomised trials (n = 2087)*


Short-term medical use of oral or oromucosal cannabis products is associated with an increased risk of non-serious, but not serious, adverse effects.


Wang T, Collet JP, Shapiro S, et al. Adverse effects of medical cannabinoids: a systematic review. CMAJ 2008;178:1669–78.

Clinical impact ratings: Family/general practice 5/7; General/internal medicine 5/7; Neurology 5/7; Oncology 5/7; Pain management 3/7


  • Source of funding: Canadian Institutes of Health Research.


The comprehensive literature review on the adverse effects of medical cannabinoids by Wang et al is an important contribution that provides clear direction for future research. The authors concluded that short-term use of cannabis for medical reasons has a reasonable safety profile. However, they noted that the effect of long-term use, especially in patients with chronic illness, is poorly researched. This review also indicated that evidence on adverse effects was not available from clinical studies in which the delivery method of cannabis for medicinal reasons was smoking.

Much of the research on side effects of cannabis has focused on recreational use in young adolescents, in whom dependence can develop.1 Other studies have shown that adolescents who use cannabis are at increased risk of psychosis, especially those who may be predisposed to mental health problems.2 However, it is unclear whether these effects are similar in older adults who use medicinal cannabis long term for symptom relief of a chronic illness.

The effectiveness of cannabinoid products for symptom management of chronic illness has been evaluated in several RCTs, with positive results. Other trials have shown that short-term use of smoked marijuana is effective for neuropathic pain.3 4

Clinicians who prescribe medical cannabis need access to current research on dose, efficacy, and adverse effects in order to provide safe and appropriate care. Given the increasing prevalence of chronic illness and the need to find alternative therapies to complement conventional symptom management, further research on the safety and efficacy of long-term controlled smoked cannabis use is essential.


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