Heavy metals, including Mercury, Cadmium, Arsenic and Lead, are toxic and exposure to them can lead to significant health issues. Limits for the presence of these toxic metals are listed in regulatory documents to minimise exposure during the medicinal use of cannabis and cannabis products.

Heavy metals in cannabis may originate from the use of contaminated water sources, soil, fertilisers and unhealthy environments, such as industrial sites and areas near mining operations. The cannabis plant absorbs these contaminants from soil and water and stores them. Ultimately these metals, if present, can transfer to humans through consumption of cannabis and cannabis products.