Quality is a particular concern, because cannabis plants easily soak up heavy metals from pesticides and other contaminants, Marcu says. If you are buying online, look for a company that documents how it tests its products. (If the website doesn’t indicate this, call and ask.) “Buying from a reputable manufacturer is crucial, because it matters how the plant is cultivated and processed,” Dr. Maroon says. One clue that a company is cutting corners: too low a cost. Good CBD is pricey—a bottle of high-quality capsules is sold in Cohen’s office for $140. But for many, it’s worth the money. Roth spent $60 on her tiny bottle. But when her energy returned the day she started taking CBD, she decided that was a small price to pay.

Basically, cannabis is an umbrella term that includes both hemp and marijuana plants. Cannabis sativa is actually the scientific name of the cannabis plant (Cannabis = genus; sativa = species), and hemp and marijuana are just two different “varieties” of it (i.e. you could refer to both marijuana and hemp plants as “cannabis” plants, but you would not, for instance, refer to a “marijuana” plant as a “hemp” plant). Hopefully that’s not too confusing.
The same terms could be applied to what's actually in CBD products. While some do contain CBD, others (often marketed as "CBD-rich hemp oil") may have barely any, Asquith says. And depending on state laws, they can include varying levels of THC too – a combination shown to have some benefits, but also drawbacks, of course, if you're not looking for a high. "People will play all these games with the numbers because the consumers aren't really educated in this space yet and it's easy to get taken advantage of," he says. "It's the milligrams of the actual CBD molecule that matter."
Dr. Devinsky’s research, which was recently published in The New England Journal of Medicine, is beginning to provide that much-needed data in the field of epilepsy research. In a landmark multinational randomized double-blind study for a treatment-resistant form of the condition, subjects taking an oral solution of 20 mg CBD per kilogram of body weight for 14 weeks, along with standard treatment, experienced a 42 percent reduction in drop seizures (the muscles go limp). Those taking a 10 mg CBD per kilogram of body weight saw a 37 percent decrease; patients who got a placebo saw a 17.2 percent decrease. The mechanism hasn’t quite been worked out yet, Dr. Devinsky says, though there’s some evidence that a receptor known as GPR55 may be critical for the anti-seizure effect.
“Marijuana and industrial hemp are different varieties of the same plant species, Cannabis sativa L. Marijuana typically contains 3 to 15 percent THC on a dry-weight basis, while industrial hemp contains less than 1 percent (Blade, 1998; Vantreese, 1998). Most developed countries that permit hemp cultivation require use of varieties with less than 0.3 percent THC. However, the two varieties are indistinguishable by appearance. DeMeijer et al. (1992), in a study of 97 Cannabis strains, concluded that short of chemical analysis of the THC content, there was no way to distinguish between marijuana and hemp varieties.” http://www.ers.usda.gov/media/328202/ages001eb_1_.pdf
Zuardi, A. W., Crippa, J. A., Hallak, J. E., Bhattacharyya, S., Atakan, Z., Martin-Santos, R., … & Guimarães, F. S. (2012). A critical review of the antipsychotic effects of cannabidiol: 30 years of a translational investigation [Abstract]. Current Pharmaceutical Design, 18(32), 5,131–5,140. Retrieved from https://www.ncbi.nlm.nih.gov/pubmed/22716160
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