This is important mainly if you want to avoid the head-high that comes with THC, something that is important to many people who are considering CBD. But knowing the THC level can be important for other reasons, too, including how effective a product might be, as well as where you can buy it.
Some research suggests that in some people, CBD may work better when it’s combined with at least a little THC, says Martin Lee, director of Project CBD, an advocacy group that supports CBD research and the author of "Smoke Signals: A Social History of Marijuana—Medical, Recreational, and Scientific" (Scribner, 2012). This is called the “entourage effect,” Lee says, the idea that the sum of the two chemicals, plus other related compounds in the plant, is greater than their individual parts.
To be sure, that notion is more theoretical than proven. And only a small amount of THC—as low as the 0.3 percent cutoff required for CBD products made from hemp—may be needed to enhance CBD’s therapeutic effect.
So if you want a product that probably has a little THC but not so much to get you high, look for one made from hemp. Such products have the added benefit of being widely available, including online and in retail stores. (Note that while Boyar and other experts say that CBD products should also include THC levels on their labels, many made from hemp don’t. For that, you need to check a product’s test results, if they are available; see number 4, below.)
Finding a CBD product that’s more than 0.3 percent THC could be tougher. For one thing, you’ll have to be in a state that has legalized marijuana, not just CBD. You’ll also need to go to a state-licensed dispensary to buy it and, in the 20 states that have legalized just the medical use of marijuana, you’ll also have to get a recommendation from a physician. In states that have legalized medical and recreational use—Alaska, California, Colorado, Oregon, Massachusetts, Nevada, and Washington—you don’t need to see a doctor first, but you do need to be over 21. (Maine and Vermont have legalized marijuana for recreational use but have yet to open recreational dispensaries.)
Dispensaries may sell a variety of “CBD-rich” products that are high in CBD and relatively low in THC, including oils, tinctures, topicals, and vaping liquids. They may even sell buds or flower from marijuana strains that have been bred to have very low levels of THC, says Michael Backes, author of "Cannabis Pharmacy: The Practical Guide to Medical Marijuana" (Black Dog & Leventhal, 2014). For example, the strain “AC/DC” can be just 0.5 percent THC, barely above the cutoff allowed for CBD from hemp and much lower than the 20 percent or higher THC concentration typical of most marijuana strains, Backes says.
Still, Lee cautions that some people are much more sensitive to the psychoactive effects of THC than others. So if you want to avoid the head-high, it's better to stick with CBD from hemp.