Cannabis contaminants: sources, distribution, human toxicity and pharmacologic effects

Br J Clin Pharmacol. 2018 Nov;84(11):2468-2476. doi: 10.1111/bcp.13695. Epub 2018 Aug 1.


There has been a resurgence in interest and use of the cannabis plant for medical purposes. However, an in-depth understanding of plant contaminants and toxin effects on stability of plant compounds and human bioavailability is needed. This systematic review aims to assess current understanding of the contaminants of cannabis and their effect on human health, leading to the identification of knowledge gaps for future investigation. A systematic search of seven indexed biological and biomedical databases and the Cochrane library was undertaken from inception up to December 2017. A qualitative synthesis of filtered results was undertaken after independent assessment for eligibility by two reviewers. The common cannabis contaminants include microbes, heavy metals and pesticides. Their direct human toxicity is poorly quantified but include infection, carcinogenicity, reproductive and developmental impacts. Cannabis dosing formulations and administration routes affect the transformation and bioavailability of contaminants. There may be important pharmacokinetic interactions between the alkaloid active ingredients of cannabis (i.e. phytocannabinoids) and contaminants but these are not yet identified nor quantified. There is significant paucity in the literature describing the prevalence and human impact of cannabis contaminants. Advances in the availability of cannabis globally warrant further research in this area, particularly when being used for patients.

Keywords: addiction medicine; cannabinoids; molecular biology; pharmacokinetics.

Publication types

  • Research Support, Non-U.S. Gov't
  • Systematic Review

MeSH terms

  • Animals
  • Cannabinoids / chemistry
  • Cannabinoids / isolation & purification
  • Cannabis / chemistry*
  • Drug Contamination
  • Environmental Exposure / adverse effects
  • Environmental Exposure / analysis*
  • Environmental Pollution / analysis*
  • Humans
  • Metals, Heavy / analysis
  • Pesticides / analysis
  • Plant Extracts / adverse effects
  • Plant Extracts / chemistry


  • Cannabinoids
  • Metals, Heavy
  • Pesticides
  • Plant Extracts