CBD is well tolerated in humans with doses up to 600 mg not resulting in psychotic symptoms (15). In the few small placebo-controlled studies performed, no significant CNS effects were noted. Oral CBD undergoes extensive first-pass metabolism via CYP3A4, with a bioavailability of 6%. Following single doses in humans, the half-life of CBD when taken orally is about 1 to 2 days.1 In vitro studies have shown that CBD is a potent inhibitor of multiple CYP isozymes, including CYP 2C and CYP3A (16, 17). Whether these in vitro observations are relevant at plasma concentrations likely to be seen in patients is unclear. In addition, given its metabolism via CYP3A4, clinical trials of CBD in patients receiving enzyme-inducing AEDs, such as carbamazepine or phenytoin, will require detailed pharmacokinetic studies.
Lisa Hamilton, a jeweler and doula in Brooklyn, NY, knows about the side effects. She recently tried CBD for the shoulder pain that plagued her five years after an accident. Her doctor certified that she was in chronic pain, which under New York State law allowed her to buy from a state dispensary. One Friday, she swallowed two 10-mg capsules, the amount recommended at the dispensary, then took another two on Saturday. “By Sunday, it felt like I’d gotten hit by a truck. Every muscle and joint ached,” Hamilton says. She cut back to one pill a day the following week, but still felt hungover. She stopped after that.
Although CBD oils aren’t regulated by the FDA, purchasing products stateside from one of the nine states where recreational and medical cannabis use is legal will likely result in a higher-quality product than buying one made with hemp-derived CBD oil imported from abroad, says Martin Lee, director of Project CBD, a nonprofit that promotes medical research into CBD.