For starters, it's entirely possible that you could consume an otherwise legal CBD product and test positive for THC on a drug screen, explains Justin Amesbury , director of research and development at Lazarus Naturals , a company that specializes in making CBD more accessible to veterans, people on long-term disability, and low-income households. Many people don't realize that almost all "full spectrum" CBD products (meaning they contain a variety of cannabinoids and terpenes) will contain trace amounts of THC, even if it claims that there's "no THC detected," he says. "This is rooted in the fact that CBD and THC are very similar molecules in terms of their physical and chemical properties, and are very difficult to separate, especially at industrial scale," he says. And, even if you're consuming a CBD "isolate" (meaning CBD has been separated from the plant), there's still a chance that it could contain THC residue that can't get washed off during the isolation process, he says.