Cannabidiol, the non-psychoactive component of cannabis, is developing a reputation as a trendy cure-all. But science knows very little about what it does in the human body, so much about the workings of this drug - including whether it works at all - is something of a mystery.
There is one exception: trials of a medical grade CBD oil called Epidiolex show that it can reduce seizures in certain types of epilepsy. An FDA committee recommended this week to approve Epidiolex as a new drug.
What is CBD?
Cannabis contains over 100 chemical components called cannabinoids. The best known of those are THC (tetrahydrocannabinol) and CBD (cannabidiol).
Meanwhile, our bodies contain receptors for cannabinoids. CB1 receptors are found mainly in the brain, and CB2 receptors are found in other types of cells, including in the immune system and digestive system. We have these receptors because we also have endocannabinoids, cannabinoids that our body naturally produces.
THC can affect the CB1 receptors, and it's responsible for weed's high. CBD is a little more complicated; it can affect both types of receptors, but often in indirect ways. The exact mechanisms aren't fully understood.
Most cannabis products contain a mix of THC and CBD, but if you're just looking for the medical effects, CBD is the portion you're interested in. It's possible to buy oils and other products that contain only CBD.
What's it good for?
There's good evidence that CBD oil can treat some forms of epilepsy. Epidiolex, a purified CBD oil made in the UK, reduced seizures by 40 per cent in trials of children with Dravet syndrome and Lennox-Gastaut syndrome. Some of the children did not respond to the drug, though. It's promising, but not a miracle cure.
Besides that, evidence is sketchy. Sellers of CBD oil tout it for dozens or hundreds of health problems. One of those, Medical Marijuana Inc, boasts that there are over 23,000 scientific papers about medical uses for CBD oil.
The only problem is that most of those papers are about pre-clinical research. In other words, it's done in test tubes or in mice. Treatments that work in mice sometimes work in humans, but this kind of research is very preliminary, and plenty of pre-clinical research hits a dead end once it's tried in humans.
So if you want to use CBD oil for your own pain, anxiety, or inflammatory conditions (like arthritis), you're making a leap of faith from those mouse studies to your own human self. Perhaps your friend has tried it and thinks it works. You might find the same - or you might not.
Experiment with caution. All our usual warnings about the placebo effect and the dangers of relying on testimonials still apply.
There's a lot of bad advice, bad science, and bad logic out there — and I'm sorry to report that some of it is probably coming from people you trust. Sharpen your pencils and take a seat — Bullshit Resistance School is in session.
What are the downsides?
Any medication that has an actual effect on your body also has the potential to have unwanted effects. CBD is no exception.
Unfortunately, the side effects are at least as poorly studied as the potential beneficial effects, so it's hard to say exactly what to expect. One 2017 review found that the most commonly reported side effects were fatigue, diarrhoea, and changes in appetite.
CBD can also affect liver enzymes, which might mean that it can change the effectiveness of other types of drugs you might be taking. The FDA committee that evaluated Epidiolex was concerned that there was a serious potential for liver injury, so patients that take the drug may need to have their liver enzymes monitored. If you're experimenting with CBD oil on your own, though, you probably don't have that option.
Another problem is that the CBD oil you order may not contain what it's supposed to. A 2017 study of 84 products sold online found that only 31 per cent contained the amount of CBD indicated on the label. Another 42 per cent were underlabeled - fine, that just means you get more for your money! — and 26 per cent contained less than the labelled content. In those cases, some contained very little of the active ingredient you're paying for. Some of the products also contained THC, even though the reason you buy CBD oil is probably that you don't want THC. (Especially if you're buying it for your sick child.)
How legal is it?
In Australia, CBD oil is a Schedule 4 drug. It's available under certain conditions from pharmacies with a valid prescription from a doctor.
In America, the answer varies from state to state. If you live in a state that has legalised cannabis for medical or recreational purposes, you're in the clear. But there are also "CBD only" states, where cannabis is otherwise illegal, but you won't get in trouble for using CBD oil. As always, check with your state for the up-to-date details.
Medical Marijuana Inc, one of the biggest sellers of CBD oil, claims that its product is legal everywhere. But the New Republic reports that the Drug Enforcement Agency doesn't buy this claim, and considers CBD oil as legally equivalent to other cannabis products. Under state laws, it's possible that CBD oil with a small amount of THC could be illegal even if the law exempts pure THC oil - so it matters what you get. And since the FDA does not and cannot regulate CBD products, nobody is enforcing the safety or purity of these products. Medical Marijuana Inc sells a "filtered, decarboxylated" version of its product that it says is totally free of THC, but it also costs more: $US165 ($215) for four ounces, versus $US119 ($155) for the raw oil.