Cannabidiol is currently a class B1 controlled drug in New Zealand under the Misuse of Drugs Act. It is also a prescription medicine under the Medicines Act. In 2017 the rules were changed so that anyone wanting to use it could go to the Health Ministry for approval. Prior to this, the only way to obtain a prescription was to seek the personal approval of the Minister of Health.
Research on low levels of CBD is, you guessed it, incredibly limited; just a single paper on the medical research database PubMed specifically looked at CBD in these low doses, as a treatment for Crohn’s disease. (It was not found to have an effect.) As such, it wouldn’t be fair to say that 5 or even 20 mg of CBD oil in your coffee is proven to do nothing; that hasn’t been proven. It’s more accurate to say that 20 mg of CBD oil in your coffee has never been proven to do much of anything, and related research indicates that’s probably way too low of a dose to have any measurable effect.
Note that the federal definition of hemp requires that it contain less than 0.3% delta-9-tetrahydrocannabinol (THC), the euphorigenic component of cannabis. And while the terms “cannabis” and “marijuana” are often used interchangeably, the Controlled Substances Act of 1970 specifically excluded the mature stalks of the cannabis plant used in industrial applications — essentially hemp — from its definition of marijuana.
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.