NCPIC - National Cannabis Prevention and Information Centre

Cannabis contamination

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What is cannabis contamination?

Over the past decade there has been increasing community concern regarding the possible contamination of cannabis. 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 product, approximately a third of Australians feel cannabis cultivated indoors is more contaminated with fertilisers, chemical sprays, growth hormones and pesticides.

Is contaminated cannabis a problem?

When the cannabis plant is being grown, contaminants may be intentionally or unintentionally added. Contamination can surface in any of three stages in cannabis production:

Contamination in cultivation

Chemicals may be added intentionally to enhance plant growth or for pest and disease control. Although chemicals added to enhance plant growth have the potential to harm users, it is not thought to be a widespread problem. Those chemicals added for pest or disease control however, are potentially more concerning. Laws exist in Australia that govern the use of pesticides, however as cannabis cultivation is illegal, the laws regarding pesticides may not be respected. Unfortunately, at present there has been no research into the extent of this potential problem.

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 commonly be Aspergillus flava, Streptococcus or Penicillium. Although it is believed that the moulds and fungi can be cleaned from the plant by flushing them with water, this is perceived to occur less often when cannabis is grown hydroponically. Although we know more about the health consequences of this type of contamination than any other, there is still little known about the extent of the problem.

Contamination in retail

Some substances can be added by retailers to increase the weight or perceived quality of cannabis. In 2004 in the United Kingdom there have been reports of glass beads being added from a spray to increase the weight of the plant and mimic the appearance of greater potency. Separate reports from Germany of lead particles being added to increase weight have also more recently appeared. These occurrences, although rare, are of great concern and have resulted in hospitalisations.

For more information please see the factsheet ‘cannabis potency’.

Factsheet published July 1, 2008. Updated October 1, 2011.