Snake Oil Cannabis? The Scientific Evidence for Medical Marijuana & CBD
What medical conditions are marijuana / cannabis and CBD (Cannabidiol) actually effective for? A round-up of the latest studies and evidence.
Use our interactive to filter & explore different medical conditions or the particular effects of CBD oil, the other major ingredient of cannabis after THC.
» See the data for more information, links & abstracts.
Part of our deeply evidence-based Snake Oil series, currently covering supplements and superfoods.
Created with our data-visualisation software VizSweet
Our Methodology & Thinking
Our evaluation is based on the latest research and studies. We score only for human trials, preferably placebo-controlled (though it’s difficult to control for cannabis due to its distinct psychoactive effects).
Many of the studies and medical claims about cannabis today are based on cell or animal studies – the effects of which rarely translate to humans.
There’s also a lot of anecdotal evidence and single case studies out there. Understandable, since people have been self-medicating with illegal marijuana for decades. But, while these stories are heartening and promising, they don’t really count as solid, scientific evidence.
The low number of human studies is due, in part, to cannabis remaining a schedule 1 drug under US federal law. Despite legalisation in several US states, much red tape and legal obstacles block those wishing to study marijuana’s medicinal effects on humans.
Not All Studies are Equal
When evaluating media reports on medical marijuana, it’s helpful to understand the different kinds of studies.
case study – WEAK – an examination of a single case of a single patient.
pilot study – WEAK but INTERESTING – small preliminary trial to test the feasibility of a treatment or justification for a larger study.
review article – INTERESTING – summarised results of existing trials and studies without any further analysis.
case control study – GOOD – specially targets and examines side-effects among populations already suffering with an ailment.
observational / epidemiological / population study – GOOD – statistical analysis of a large populations for patterns & effects over time, but hidden factors may influence perceived results.
controlled / clinical trial – GOLD STANDARD – randomly selected groups of people given either an active substance or a non-active ‘placebo’. Ideally ‘blind’ so neither the subjects nor the experimenters know who’s receiving placebo.
meta-analysis / meta study – VERY GOOD – critically examines & re-evaluates all existing trials & studies and mashes the results to look for consistencies & patterns.
(Cochrane is the gold standard)
This is an ongoing, evolving graphic. So let us know if we’ve missed any studies or conditions. Please cite your sources.
What conditions are medical marijuana / cannabis & CBD (Cannabidiol) actually effective for? A round-up of the latest scientific studies and evidence in one infographic.
CBD oil: miracle cure or snake oil?
Derived from the cannabis plant, CBD oil is touted as a cure for everything from joint pain to epilepsy, with the global industry estimated to be worth almost £800 million. But is it effective?
Published: 30th July, 2019 at 20:00
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What is CBD oil?
The cannabis plant, Cannabis sativa, contains a number of active ingredients, including THC and CBD. THC (tetrahydrocannabinol), the most active ingredient of marijuana, is the component that makes a person high when either smoked or ingested. Cannabidiol (CBD), on the other hand, is not psychoactive: it doesn’t induce a mind-altering effect.
CBD oil is a way of delivering CBD. This chemical is first extracted from the plant and then diluted with a carrier oil like hemp seed. It can then be consumed as either the oil itself or within drinks or confectionary. In the UK, it can be found in health shops.
How does CBD work?
The human body has two currently-known types of points where cannabinoids can bind, called CB1 and CB2 receptors. Cannabinoids can attach to the CB1 and CB2 docking points since they have a similar structure to the body’s naturally-occurring endocannabinoids. From here, CBD can impact movement, pain, emotions, mood and other functions regulated by endocannabinoids. This is still an area of active research and much of how it all works is still being explored.
Is CBD Legal?
The vast majority of cannabinoids, listed as controlled substances under the Misuse of Drugs Act, are illegal.
However, CBD derived from industrial hemp that is EU-approved is completely legal in the UK, under certain conditions. The strain must contain no more than 0.2 per cent THC, and the THC must not be easily separated from it. By contrast, cannabis oil, which has a higher THC content, is not legal.
With the change of law in November 2018, specialist clinicians are allowed to prescribe cannabis-derived medicinal products for some patients with multiple sclerosis or epilepsy. However, cannabis-derived products including CBD oils available to buy over the internet are unlikely to meet the required standards, making them illegal and potentially dangerous.
Is CBD oil effective?
Many users of CBD oil claim it helps to relieve pain and inflammation, reduce anxiety and make them calm. Currently, scientific studies cannot say whether the small CBD quantities available in CBD products have any effect at all, but that hasn’t held back use. This is an area of ongoing research – we just haven’t reached a point where we have all the answers. Science is working to catch up with the demand.
CBD products available in health food shops and on the internet are not controlled or regulated as medicines, other than the legal limit on THC content. As doctors, we are advised to tell patients that ‘over-the-counter or internet’ CBD products lack quality assurance and should not be treated as medicines. There’s no way to be sure of what’s in the products you buy.
What conditions can CBD oil help?
The list of things we’re told CBD oil can do for us is long, but there is still only preliminary evidence.
There is some belief that CBD is a natural painkiller. It’s also thought to have anti-inflammatory properties, and so it may help as a treatment for inflammatory diseases like Crohn’s disease. Indeed, some small studies in mice have supported this claim by showing that CBD significantly reduced chronic inflammation and pain. This has led hope that it may one day help chronic pain, but we won’t know until human tests are complete.
CBD is also believed to help people who suffer from anxiety and mood-related symptoms, as well as insomnia.
The condition that brought CBD oil to prominence is epilepsy. Scientific reviews have found that CBD has anti-seizure properties and there are several clinical trials well underway, some of which use pure CBD product. Stronger forms of CBD have been found to reduce the number of epileptic seizures suffered by some patients by more than 40%.
This has resulted in parents of children suffering with severe epilepsy buying illegal forms of high-strength cannabidiol CBD oil online. But this carries risk.
Initial research in mice published in the Journal of Alzheimer’s Disease found that CBD may one day help people in the early stages of the condition by helping them keep the ability to recognise the faces of people that they know. Undoubtedly the impact of cannabis-based treatment on Alzheimer’s is an exciting new, promising area. Researchers from the National Institute for Health Maudsley BRC are conducting a study to see if cannabis-based treatment containing CBD can ease symptoms of agitation and aggression in patients with Alzheimer’s, where at the moment treatment options are limited. Still, it’s early days.
Derived from the cannabis plant, CBD oil is touted as a cure for everything from joint pain to epilepsy. But is it effective?