Does CBD lower blood pressure? What was measured

The study everyone quotes

In 2017 a group at the University of Nottingham published a randomised crossover trial in JCI Insight. Nine healthy men received a single 600 mg dose of CBD or a placebo, and their cardiovascular measurements were taken at rest and under stress. Resting systolic blood pressure was around 6 mmHg lower after CBD, with a compensating rise in heart rate and a smaller rise in blood pressure under stress.

That is a real, measured effect, and it is the source of virtually every claim made about CBD and blood pressure. Two things about it are usually left out of the retelling.

• Nine people. All of them men, all of them healthy, none of them hypertensive.
• One dose. The measurements were taken over hours, not weeks, so the study says nothing about what happens if you keep taking it.

What happened when they kept taking it

The same research group answered that second question in 2020, in the British Journal of Clinical Pharmacology. Twenty-six healthy men were randomised to CBD or placebo for seven days, with haemodynamic measurements on day one and day seven.

This is the ordinary shape of a physiological response: the body adjusts. It is also why single-dose studies are a starting point rather than a conclusion, and why the gap between the two papers is the most informative thing on this page.

What has not been measured

Nobody has run a randomised trial of CBD in people with diagnosed hypertension, measured over the months that blood pressure management is actually judged over. That is the trial that would answer the question this page is named after, and it does not exist.

So the honest position is narrow: in small numbers of healthy young men, a large single dose moves a number for a few hours. What that implies for a person on antihypertensives, or a person whose readings sit just above the threshold, has not been established by anyone.

What blood pressure responds to

The 6 mmHg figure above is only meaningful next to something. The 2017 American College of Cardiology and American Heart Association guideline puts approximate numbers on the changes that have been measured repeatedly in people who actually have raised blood pressure, and they are the right comparison to hold the CBD result against.

Every row in that table has been measured over months in people with hypertension and holds up when the behaviour holds up. The CBD figure was measured over hours, in nine healthy volunteers, and was absent again after a week of dosing in the follow-up study. They are not the same kind of number, and putting them in the same sentence without saying so is how this topic usually goes wrong.

Why interactions matter more here

Blood pressure is usually managed with medicines, and that makes this topic different from most CBD subjects, where the main risk is to your wallet.

CBD inhibits cytochrome P450 enzymes in the liver, and those enzymes metabolise a long list of commonly prescribed drugs. Inhibiting them raises the blood level of the other medicine without anything else changing. A compound that lowers blood pressure a little on its own, taken alongside a medicine whose level it may raise, is a question for a pharmacist rather than an article.

Why a home reading is not the answer

Blood pressure is not a fixed property of a person. It moves through the day, rises with a full bladder, a conversation, a cup of coffee or the ten minutes before a nurse takes it — the last of which is common enough to have its own name, white-coat hypertension. Diagnosis rests on repeated readings for that reason, often with a monitor worn for a day or an agreed week of readings at home.

• One reading is close to meaningless, high or low, and a single reading taken after starting something new is the least informative of all.
• Sit still for five minutes first, feet on the floor, arm supported at heart height, cuff on bare skin and the right size for your arm.
• Take two or three readings a minute apart and record all of them, morning and evening, over a week.
• Bring the whole record, not a summary of it. The pattern is what a clinician reads; the average is only part of it.

The practical point for this topic: a week of readings that look better after starting a supplement is exactly what the ordinary movement of the number looks like. That is what a placebo-controlled trial exists to separate out, and what an individual cannot separate out alone.

Reading a label without being taken in

The doses in both studies above were 600 mg, given as a purified pharmaceutical-grade product. A 2017 analysis in JAMA of 84 CBD extracts bought online found around seven in ten were inaccurately labelled, some with measurable THC that was not declared — and THC raises heart rate, which is the one thing worth avoiding on this topic.

What this page will not tell you

It will not give you a dose, because no dose has been established for this purpose and printing a number would imply one has.

It will not tell you CBD lowers blood pressure in the sense anyone means by that phrase — as something you could rely on over months. One acute effect in nine healthy men, absent again after a week in a second study, is not that.

It will not tell you to dismiss the topic either. The acute finding is real and was replicated on day one of the second study. If a longer trial in people who actually have hypertension is ever run, it will be worth reading, and this page will say what it found.