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Green tea and beta blockers

The BBC published an article a few days ago titled “Green tea ‘can impede nadolol blood pressure medicine’” It represents some pretty sloppy health reporting. Let me expand, bit by bit.

Green tea can weaken the effects of a commonly prescribed blood pressure pill, experts warn.

We’re off to a bad start. Right from the first sentence of the article, we have a glaring error.

The drug in question is called nadolol, which is a beta blocker from the same family as atenolol and propranolol. The chances are you’re familiar with one of those drugs, but not with nadolol, and there’s a very good reason for that – nadolol is not commonly prescribed as claimed by the BBC. In fact, it’s barely prescribed at all. The evidence for that is publicly available; the Health and Social Care Information Centre (HSCIC) is a UK body which regularly publishes statistics on drugs prescribed in England. The latest set was published on the 4th of April 2013, and details everything prescribed in 2012 – an awful lot of drugs. You can get a copy for yourself here.

The HSCIC data tell us that in 2012 there were 32,355,600 prescriptions dispensed for beta blockers. Those figures include 11.5 million prescriptions for atenolol, 14 million for bisoprolol and over 3.5 million for propranolol. How many prescriptions for nadolol? Seventeen thousand. That means that nadolol accounted for 0.05% of all the beta blocker prescription items dispensed in England in 2012. I don’t think that 0.05% of anything can ever be described as “common”.
One important thing to note about the prescribing data is that it doesn’t tell you how much of each drug a prescription represents – some might have been for a four weeks supply, some might have been for 12 weeks. However to change the figures above, each nadolol prescription would need to have been for several years supply, which isn’t something that happens.

The next problem with the BBC article is this:

The study in the journal Clinical Pharmacology & Therapeutics found nadolol’s lowering effect on blood pressure was blunted in the 10 volunteers who agreed to drink green tea.

Ten volunteers. Ten. Volunteers. Neither of these words is good in terms of clinical research. If I were evaluating a drug and saw a trial with ten people in it, I would only take the evidence into account if there was no larger, randomised trial available. In fact, if a trial in ten volunteers was the only available data I still might not read it; my recommendation would be along the lines of “we do not know enough about this drug to use it safely; we need more evidence”. The burden of proof for a safety issue is clearly lower, so that’s not the best analogy, but the fact remains that the sample size is not sufficient for the level of fuss that’s been caused here. It’s also worth noting that these were *healthy* volunteers. How do we know that the same thing would happen to a person who was unwell and required a beta blocker?

Follow-up tests in the laboratory revealed that green tea blocked a drug transporter present in the lining of the human gut that helps move nadolol into the cells.

Well. Kind of. Follow-up tests were done in a laboratory, but not in human guts. The tests were done on cells, in a petri dish, on a cell line called HEK293, which were originally derived from Human Embryonic Kidney. Although they are kidney cells they’re probably not very useful for telling you what would happen in a living, adult kidney. It maybe doesn’t matter too much what the cells are as long as the drug transporter involved is the right one, but I’d expect more clarity from the BBC.

So the end result is that some scientists found that drinking green tea makes a drug that is very rarely prescribed work a bit less well, probably, in healthy volunteers. Let’s be clear: that’s a perfectly adequate conclusion for a scientific study – it’s tiny nuggets like this that are the building blocks of good medicine. The problem here is the quality of the reporting on the issue. Very little additional time, effort or words would have been needed to make the article much more representative of the real impact of the findings.

If you’re a regular green tea drinker who takes nadolol, the chances are that your dose has been adjusted to suit you already, through a process of your doctor checking your blood pressure and tweaking the dose. If you’re an occasional green tea drinker, you probably have nothing to worry about, but you can minimise any risk by leaving several hours between taking your pills and drinking any tea. It’s very important to realise that if there is any risk (and we can’t be sure by any means from a study of ten healthy people), it’s likely to be minimal. If you’ve any worries at all, have a chat with a local pharmacist or your doctor.

And the next time you see a story like this, don’t immediately take it at face value.

Edit: it’s worth mentioning that this study tells us nothing about other beta blockers. They might be affected in the same way, they might not – we won’t know until someone takes the time to do the experiments. If you’re concerned about a drug other than nadolol, and your habits haven’t changed lately, it’s unlikely you have anything to worry about. If you have any worries at all, your pharmacist or doctor will be happy to discuss them with you.