Sativex, a cannabis plant–derived oromucosal spray containing equal proportions of THC and CBD, has been approved in a number of countries for use to treat specific types of pain. Numerous randomized clinical trials have demonstrated the safety and efficacy of Sativex for treatment of central and peripheral neuropathic pain, rheumatoid arthritis, and cancer pain. 
But, uh, what is it that CBD is supposed to do? I visited a cannabis dispensary in Boulder to find out what the hype was all about. After passing an ID check, I was introduced to a “budtender” who pointed me to an impressive array of CBD products — tinctures, skin patches, drink powders, candies, salves, massage oil, lotions, “sexy time personal intimacy oil” and even vaginal suppositories to treat menstrual cramps.
In the U.S., we live in a culture where more is often perceived as being better. And it’s easy, without even thinking about it, to apply that approach to CBD dosing. But when it comes to CBD, more is not necessarily better. In fact, for many, less CBD is more effective. One way to determine your optimal dosage is to start with a small amount of CBD for a couple weeks and then slowly increase your dosage, carefully taking note of symptoms, until you’re seeing the results you want.
Using CBD in defined doses for medicinal purposes is one thing, but putting it in food and beverages is something entirely different. Someone may wind up getting CBD from multiple products, and so their daily dose could vary significantly. Taking a standardized dose of CBD oil daily as a recognized medicinal is a very different thing from taking uncontrolled doses of CBD isolate daily infused artificially into food and beverage products, and the long term risk may be very different — no one really knows for sure.
Could cannabidiol help prevent tumors and other cancers before they grow? A 2012 study showed that animals treated with CBD were significantly less likely to develop colon cancer after being induced with carcinogens in a laboratory. Several studies had already shown that THC prevents tumors and reduces them, including one in 1996 on animal models that found that it decreased the incidence of both benign and hepatic adenoma tumors. In 2015, scientists analyzed the medical records of over eighty-four thousand male patients in California and found that those who used cannabis, but not tobacco, had a rate of bladder cancer that was 45 percent below the norm. Topical products can be used to treat and prevent skin cancers. Continuing research is focused on the best ratio of CBD to THC and the most effective dose level in cancer prevention and treatment.