Health Canada claims it has put into place “some of the most stringent controls on the medical cannabis industry in the world.”1 Under these regulations, only specific pesticides and fungicides are registered for use by licensed cannabis producers. But as of March, 2017, three class-action lawsuits had been launched in Canada by people who claim to have experienced adverse health effects from using medical cannabis products contaminated with unauthorized pesticides.2

In February, 2017 Health Canada began unannounced inspections and random testing of cannabis products from licensed producers to ensure only registered pesticides were used in safe amounts. Out of the first seven random tests, two sites had contaminated samples.3 In May, 2017, Health Canada enhanced the stringency of its regulations by requiring all licensed producers to conduct mandatory testing for unauthorized pesticides.

But problems continued. On August 19, 2017, the Globe and Mail ran a story about a retired military veteran who was hospitalized seven times over a span of six months for shortness of breath, mysterious rashes, muscle aches and coughing.4 It took six months before it was determined his problems were linked to the medical cannabis he had been prescribed to treat pain from a serious back injury. But it took several more months before the company supplying his cannabis revealed that during the previous year their products had been laced with two banned pesticides: myclobutanil, a fungicide used to kill mildew, and bifenazate, an insecticide.

Subsequent testing by the Globe and Mail of a sample of the veteran’s cannabis showed not only the two reported pesticides but an additional three banned products. (Note: these findings of additional contaminants were not substantiated by Health Canada tests and have been disputed by the producer. None of these claims have been proven in court.)

If medical cannabis is to be safe, we must ensure unauthorized pest control products are not used and authorized products are used in safe amounts. Unfortunately, there are few evidence-based guidelines to inform regulations. In the U.S., for example, regulations vary greatly between states: Massachusetts, for example, bans all non-organic pesticides while Nevada, Oregon and Washington have strict limits on how much pesticide residue is allowed and require testing before products can go on sale, and California has no regulations.5

Pesticides allowed by some jurisdictions for use on medical cannabis were almost exclusively designed for, and tested on, food crops. With the exception of pesticides used on tobacco, little testing has been conducted to determine safety when a product is used on plant matter that is ignited or inhaled, ingested in the form of baked goods, or delivered as eye drops, skin lotions or suppositories. Extracts that are smoked or vaporized may concentrate not only the active ingredients of cannabis (e.g., THC and other cannabinoids) but also any pesticide residues that may be present.

As one commentator explains, “To take a pesticide through a trial in order to certify it for cannabis use can take three years [and] that involves a huge number of studies and 10-20 million dollars and then some.”6 In the U.S., the Scotts Miracle-Gro company tried to register pesticides for use on cannabis with the Environmental Protection Agency (EPA) but was rebuffed in June, 2017, on the technical grounds that cannabis continues to be federally illegal product.7

In an article in Smithsonian magazine, Andy LaFrate, a founder of a Colorado lab certified to test cannabis, was quoted as saying, “There’s a stereotype, a hippy kind of mentality, that leads people to assume that growers are using natural cultivation methods and growing organically. That’s not necessarily the case at all.”8 And pesticides aren’t the only problem – LaFrate reports his team commonly finds fungi and bacteria in the products they test. Concentrates and edibles may not require smoking but some manufacturers use potentially harmful compounds like butane to extract the THC.

What if a patient decides to grow their own medical cannabis? For the authorized home producer, Health Canada advises, “If you plan to use chemical products, such as pesticides, ensure that these products are safe for use on a plant that you plan to eat or vaporize.”9

However, the link for more information, Homeowner Guidelines for Using Pesticides, provides only general information and does discuss the unique challenges of medical cannabis.11 If a home producer wants to have their cannabis tested by an authorized lab, he or she must cover the cost.10 Depending upon the number and type of tests conducted, this may cost the home producer from a few hundred dollars to up to $1,000 per sample.

We expect Health Canada to ensure that a wide range of products – from packaged meats to pharmaceuticals – are safe. It’s not unreasonable to expect the same for medical cannabis. But to perform this task, Health Canada needs evidence on the health effect of pest control products, systems for ensuring testing is conducted in a timely fashion, and regulations to enforce rapid and comprehensive recall of unhealthy products. Systematic research will be essential to address these questions.

Author Details

The latest scientific evidence on this topic was reviewed by the Centre's leadership team. This evidence brief is written by Corinne Hodgson, DHealth, assessed for accuracy by Co-Director Dr. James MacKillop, PhD, an expert in addictions and mental health research. There are no conflicts of interest. Questions regarding this piece should be directed to Dr. James MacKillop (

  1. Clarification from Health Canada on myclobutanil and cannabis. Statements. Health Canada. Date modified: 2017-03-09

  2. Robertson G. Pesticide-laden medical marijuana spurs third Canadian lawsuit. The Globe and Mail. March 14, 2017

  3. Statement from Health Canada on Mandatory Testing of Medical Cannabis for Unauthorized Pesticides. Health Canada, May 5, 2017.

  4. Robertson G. They turned to cannabis for relief. But after getting sick, patients are fighting for answers. The Globe and Mail, August 19, 2017.

  5. Grover J, Glasser M. Pesticides and Pot: What’s California Smoking? NBC Los Angles. February 23, 2017.

  6. Subritzky T, Pettigre S, Lenton S. Into the void: regulating pesticide use in Colorado’s commercial cannabis markets. Inter J Drug Policy 2017;42:86-96

  7. Kaskey J. Pot laced with pesticides forces states to act as EPA stay away. BloombergPolitics. August 2, 2017.
  8. Handwerk B. Modern marijuana is often laced with heavy metals and fungus. March 23, 2015.
  9. Information bulletin: safety and security considerations when producing cannabis for your own medical purposes. Health Canada.
  10. Homeowner Guidelines for Using Pesticides. Health Canada
  11. Licensed dealer testing of cannabis produced by individuals. Health Canada.