California is currently grappling with how to regulate pesticide use on cannabis. There is an obvious need to ensure that users – especially medical patients – are not endangered by pesticide contamination. In most states, however, the allowable limit of pesticides on cannabis has not been guided by safety. Because relatively little is known about pesticide toxicity in humans, pesticide limits are often set as what is “reasonably achievable by analytical chemists.” 1 In other words, the allowable concentration of pesticides is based on the ease of detecting chemicals rather than a prioritization of their dangers. This has the risk of pushing growers away from relatively safe but easily detectable pesticides, towards stronger pesticides that are potentially more dangerous.

The two pesticides pyrethrins and myclobutanil have highlighted many of the problems of current pesticide regulations. The allowable limit of pyrethrins on cannabis products is 1 part per million (1 ppm) in most states, meaning that up to 0.0001% of the product by weight can be pyrethrins. The European Food Safety Administration has suggested that 0.4 mg per kg bodyweight is a safe daily dose of pyrethrins. At the 1 ppm limit, this means that an average 135 pound individual could ingest 55 pounds of cannabis products with 1 ppm pyrethrins before pyrethrin toxicity becomes an issue 2. Even if the limit were raised to 40 ppm, an average adult could eat over a pound of cannabis without toxicity due to pyrethrins. This indicates that the regulation of pyrethrins – at least in comparison to other pesticides – is absurdly strict.

Myclobutanil (often sold as Eagle-20) has exposed the importance of how people administer cannabis. When heated, this pesticide degrades into hydrogen cyanide – a potent toxin that causes neurological damage at 0.008 ppm 3. Although some states have now banned myclobutanil use on cannabis, Nevada allows it at concentrations up to 9 ppm (nine times higher than the pyrethrin limit). Because smoking and vaporizing are still the most common methods of administering cannabis, it is essential to understand the breakdown products of pesticides. But there is very little information available on the effect of burning pesticides.

In contrast to myclobutanil, pyrethrins likely decompose to two safer compounds – chrysanthemic acid and a rethrolone – when heated without burning, as happens in a vaporizer. That said, it is not clear what the breakdown products are when pyrethrins are burned, or how hazardous these may be.

We are not opposed to regulations, least of all safety regulations around cannabis. But a blanket opposition to all pesticides may push growers towards more potent pesticides, which could be more dangerous to humans. It is essential to study the toxicity of heating pesticides to the temperatures of a vaporizer (around 200 @C) and joint (around [email protected]). In the meantime, regulations should be set based on our current understanding of the relative safety of pesticides.

Reprinted with permission from Project CBD.


  1. Guidance for State Medical Cannabis Testing Programs. Association of Public Health Laborotories. 2016. Link
  2. Conclusion on the peer review of the pesticide risk assessment of the active substance pyrethrins. EFSA Journal. 2013. Link
  3. Material Safety Data Sheet: Eagle 20EW - Specialty Fungicide. Crop Data Management Systems. 2012. Link

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