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That changed Friday, when Health Canada said mandatory pesticide testing was necessary to “ensure that Canadians can continue to have confidence in obtaining safe, quality-controlled medical cannabis.”

Only 17 pesticides are approved for use on cannabis, the department warned in a statement. “There are no exceptions to these requirements, and no situations in which using a pesticide that is not authorized … for cannabis cultivation would be acceptable.”

Concern has been growing in the past several months after three marijuana producers recalled products found to contain unapproved pesticides, including myclobutanil. Some patients who say tainted marijuana made them sick have joined three class-action lawsuits now seeking certification in the courts.

Myclobutanil has been used by illegal pot growers to control mildew. The pesticide is approved for use on some fruits and vegetables, but not for plants that are dried and smoked.

Health Canada maintained that the levels of myclobutanil found in the recalled products from legal producers would not cause serious health problems. But officials also stepped up enforcement. In March they began a series of random, unannounced inspections to test plants, dried weed, cannabis oils and pest-control products for unapproved pesticides.

Test results from plant samples taken at seven sites came in this week revealed the problems at Hydropothecary and Peace Naturals. Plants at the five other companies showed no signs of pesticide contamination, said Health Canada. They are Tweed in Smiths Falls, RedeCan and 7 Acres in Ontario, and Tilray and Broken Coast in B.C. Results of tests on dried weed and oils at the seven sites aren’t available yet.