Recreational or medical marijuana is legal in most states in the U.S. If you live in one of those states and choose to use marijuana, here are some things to consider. Don't trust labels “You can’t rely on labels,” says Daniele Piomelli, professor of anatomy and neurobiology at the University of California, Irvine. In states that test cannabis products, the results are troubling. For example, in 2018 the California Bureau of Cannabis Control tested nearly 26,000 products—plant material, vape pen cartridges, waxes, oils, tinctures, topical creams, edibles—sold at dispensaries. Almost 15 percent failed tests for potency or purity, typically because they were mislabeled or had detectable levels of pesticides, microbes, or solvents.