Cannabis Contamination

What is cannabis contamination?

Concern over the possible contamination of the cannabis product is widespread across Australia1. The contamination being referred to is the intentional or unintentional addition of potentially harmful substances to the cannabis plant, usually added to enhance the actual or perceived plant growth and quality.

Even though cannabis is usually perceived to be a natural or chemical free product2, approximately a third of Australians feel cannabis cultivated indoors is more contaminated with fertilisers, chemical sprays, growth hormones and pesticides1.

Is contaminated cannabis a problem?

When the cannabis plant is being cultivated, contaminants may be intentionally or unintentionally added3. Contamination can surface in any cultivation technique in any of three stages; in cultivation, storage and/or in retail.

Contamination in cultivation

Intentionally added chemicals include those added to enhance plant growth or for pest and disease control. Although chemicals, such as nitrogen and potassium, added to enhance plant growth have the potential to harm users, it is not thought to be a widespread problem. The harm is restricted to cannabis grown in areas with heavy metal content in soil3. However, those chemicals added for pest or disease control are potentially more concerning. Laws exist in Australia that govern the use of pesticides4, however as cannabis is an illegal drug, there are no such guidelines for its cultivation. Unfortunately, at present there has been no research into the extent of this potential problem. Interestingly, one Dutch study has shown traces of pesticides in cannabis, but not in an amount likely to cause harm5.

Contamination in storage

While cannabis is being stored (during cultivation or by the user) certain types of moulds and fungi may unintentionally grow on the plant. These moulds have been identified to usually be Aspergillus flava, Streptococcus or Penicillium3. This type of contamination has been identified in Dutch coffee shops6. Although it is believed that the moulds and fungi can be cleaned from the plant by flushing them with water, this is perceived to be less likely in indoor cultivation7. The health consequences of this type of contamination remain to be adequately researched.

Contamination in retail

Some substances can be added by retailers to increase the weight or perceived quality of cannabis. Recently in the United Kingdom there have been reports of glass beads being added to increase the weight of the plant and mimic the appearance of greater potency8. Separate reports of lead particles being added to increase weight have also more recently appeared9. These occurrences although rare, have resulted in hospitalisations and shortly after, the UK Department of Health issued a public health warning10.


  1. StollzNow. (2006). Market research report: Australians on cannabis. Report prepared for NDARC and Pfizer Australia. Sydney: StollzNow Research and Insights Advisory.
  2. Hall, W. & Nelson, J. (1995). Public perceptions of health and psychological consequences of cannabis use. Canberra: Australian Government Publishing Service.
  3. McPartland, J. M. (2002). Contaminants and adulterants in herbal cannabis. In F. Grotenhermen & E. Russo (Eds.), Cannabis and cannabinoids: Pharmacology, toxicology, and therapeutic potential (pp. 337 343). New York: Haworth Press.
  4. Australian Pesticides and Veterinary Medicines Authority. (2004). Chemicals and food safety: Information sheet. Canberra: Australian Pesticides and Veterinary Medicines Authority.
  5. Trimbos Institute. (2006). The Netherlands National Drug Monitor. Annual Report 2005. Utrecht: Trimbos Institute.
  6. Hazekamp, A. (2006). An evaluation of the quality of medicinal grade cannabis in the Netherlands.Cannabinoids 1, 1 9.
  7. Swift W., Gates, P. & Dillon, P. (2005). Survey of Australians using cannabis for medical purposes.Harm Reduction Journal 2, 1-10.
  8. UK Cannabis Internet Activists. (2007). Cannabis contamination. Retrieved 28 June 2007, from
  9. Busse, F., Omidi, L., Leichtle, A., Windgassen, M., Kluge, E., & Stumvoll, M. (2008). Lead poisoning due to adulterated marijuana. New England Journal of Medicine 358, 1641 1642.
  10. Department of Health. (2007). Alert contamination of herbal or skunk-type cannabis with glass beads. Retrieved 29 June 2007, from

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