Side effects and safety concerns:
CBD can cause side effects and interact with certain medications and conditions, although these effects have typically been reported only with very high daily intake, i.e., hundreds of milligrams daily.
High daily doses of CBD (20 mg per kg of body weight, i.e., hundreds of milligrams) may cause decreased appetite, diarrhea, vomiting, fatigue, fever, somnolence, and abnormal results on liver-function tests (Devinsky, New Eng J Med 2017; Thiele, Lancet 2018).
CBD at a dose of 300 mg has been shown to worsen symptoms of Parkinson's disease (Consroe, Int J Neurosci, 1986).
CBD should be used with caution with sedative and sleep-inducing medications, as it may enhance their effects.
CBD can increase blood serum levels of antiepleptic drugs (Gaston, Epilepsia 2017).
CBD may increase the blood-thinning effects of warfarin (Coumadin, Jantoven) likely because CBD competes for the same liver enzymes that break down warfarin and other drugs. This was observed in a man with post-stroke epilepsy taking warfarin: His INR (a measure of how long it takes blood to clot) began increasing several weeks after starting CBD (Epidiolex, Greenwich Biosciences, Inc.) for his seizures. His CBD dosing started with several hundred milligrams daily and increased to over 1,000 mg, at which point his warfarin dose had been reduced by approximately 30% (Grayson, Epilepsy Behav Case Rep 2017).
Another cause for concern is the unreliability of the purity and dosage of CBD in products. A recent study of 84 CBD products bought online showed that more than a quarter of the products contained less CBD than labeled. In addition, THC was found in 18 products.
If you plan to use products containing CBD, talk to your doctor.
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