Almost every health claim made about CBD traces back to a real study. The trouble is that studies are not all equal. A result in a dish of cells is a long way from proof that an oil helps a person. Our grades are a quick way to see how far the evidence for each use has actually come.
The five grades
| Grade | What it means |
|---|---|
| Strong evidence | Large, well-run randomised controlled trials agree, and regulators have approved a CBD medicine for this use. |
| Moderate evidence | Several controlled trials in people point the same way, but they are small, short or not yet confirmed. |
| Limited evidence | A few small or early human trials, or mixed results. Not proven. |
| Not enough evidence | Mostly laboratory work, animal studies, surveys or individual reports. No good human trials yet. |
| Trials show no benefit | Controlled trials have tested CBD for this and found it no better than placebo. |
What counts as good evidence
Researchers rank study types by how well they rule out other explanations. From strongest to weakest:
- Systematic reviews and meta-analyses. These gather every good trial on a question and weigh them together.
- Randomised controlled trials (RCTs). People are randomly given CBD or a placebo, ideally without anyone knowing who got which until the end. This is the fairest test of whether a treatment works.
- Observational studies. Researchers follow people who chose to take CBD. These cannot separate the effect of CBD from the placebo effect, or from the fact that many conditions improve with time.
- Case reports and surveys. Useful for spotting ideas to test. Not proof.
- Animal and laboratory studies. Essential early science, but most treatments that work in mice or cells fail in people.
Why placebo control matters so much
Pain, anxiety and sleep all respond strongly to expectation. In trials for these conditions, people given a dummy oil often improve a lot. A treatment has to beat that improvement to count as working. This is why an uncontrolled study reporting that most patients improved tells you very little: you do not know how many would have improved anyway.
It also explains why personal stories are weak evidence, however sincere. The person may truly feel better. The story cannot tell you whether CBD was the reason.
CBD is not the same as cannabis
Many studies of “medicinal cannabis” used products containing THC, the compound that causes a high, alone or mixed with CBD. THC and CBD act differently in the body. A trial showing that a THC product eased a symptom is not evidence that CBD does. We grade only the evidence for CBD, and where a page discusses a mixed product we say so.
Dose matters
Trials that reported an effect of CBD have mostly used hundreds of milligrams a day, and sometimes more than a thousand. Many consumer products contain far smaller amounts. Evidence at a high dose is not evidence at a low one, so each condition page states the doses that were tested.
What a low grade does and does not mean
“Not enough evidence” means the question is open. Nobody has run the trials needed to know whether CBD has any effect.
“Trials show no benefit” is different. It means the fair test has been run and CBD did not beat placebo.
Neither grade is a comment on your own experience. Both are a statement about what can honestly be claimed.
Grades change
New trials keep being published. When good new evidence arrives, we change the grade and the date at the top of the page.
This page is general information, not medical or legal advice. Laws and evidence change; we show the date we last checked the facts at the top of every page. Talk to your doctor or pharmacist before starting, stopping or changing any medicine.
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