What vitamins should you not take with HRT?

If you've started HRT and you're already taking something from the supplement aisle, it's a fair question. Most of us assume that anything sold next to the multivitamins is, by definition, harmless.

The short answer is that vitamins are rarely the problem. Herbal supplements are. And one in particular is worth knowing about.

St John's wort is the one that matters

St John's wort is sold over the counter and often taken for low mood — which is exactly why women going through menopause end up taking it. It's also the supplement with the clearest interaction picture.

The mechanism is straightforward once you know it. St John's wort speeds up the liver enzymes that break down certain drugs. If your body clears a hormone faster, less of it is available to do its job. The result is that HRT can quietly become less effective, and there is no obvious signal that this is what's happening. It just feels like the HRT isn't working.

NICE guidance, as summarised in NHS prescribing guidance, notes that St John's wort may interact with other drugs including tamoxifen, anticoagulants and anticonvulsants. The same guidance flags a second problem: there is uncertainty about the appropriate dose, and the potency of over-the-counter preparations can vary. Two bottles from two shops are not necessarily the same product.

If you take St John's wort, it belongs on the list you give your GP or pharmacist — the same as any prescribed medicine.

If you've had breast cancer, the list is longer

This is the group where the guidance is most specific.

NHS prescribing guidance states that isoflavones, red clover, black cohosh and vitamin E are not recommended for people who have had breast cancer, and notes that most herbal supplements haven't been tested in people with a history of breast or oestrogen-sensitive cancers. It advises referral to a menopause-oncology clinic where appropriate.

If that's you, this isn't an article to make decisions from. It's a conversation to have with whoever is looking after you.

The bigger point: supplements aren't regulated like medicines

This is the part that tends to surprise people, and it's worth stating plainly.

NHS Somerset's prescribing guidance puts it directly: health food supplements may vary, their safety is not regulated in the way medicines are, and interactions may be possible. It reminds healthcare professionals to stay alert to adverse reactions from herbal and homeopathic products and to report suspicions through the MHRA's Yellow Card scheme.

That's an NHS document telling clinicians to treat supplements as an unknown quantity. It doesn't mean supplements are dangerous. It means "it's natural" and "it's been tested" are not the same sentence, and the second one often hasn't happened.

The same guidance is even-handed about the other side of this: it notes there is some evidence that isoflavones or black cohosh may relieve hot flushes and night sweats, and treats them as reasonable for self-care. So this isn't a case of herbals being useless. It's a case of them being genuinely medicinal enough to interact — which is the same reason they might work at all.

So what about actual vitamins?

Here is where we part company with most of what's written on this subject.

Search this question and you'll find pages — often on supplement retailers' own sites — stating that high doses of vitamin C or vitamin B6 interfere with how the body handles oestrogen. We could not find that claim traceable to NHS, NICE or MHRA guidance. We're not saying it's false. We're saying we couldn't source it, and by our own standards that means it doesn't go in as fact.

What we can say is that the UK guidance on supplements through menopause is mostly about getting enough of the right ones rather than avoiding them. Vitamin D is the clear example: UK adults are advised to consider a daily 10 microgram supplement, and it's the one supplement the British Menopause Society recommends as standard through perimenopause and menopause. Nobody suggests stopping it because you've started HRT.

If you want the detail on what's actually worth taking, we've written about what the evidence says on menopause supplements separately.

What to actually do

Three things, and none of them require a decision from you about pharmacology.

Write down everything you take. Not just prescriptions — the vitamin D, the magnesium, the thing your sister recommended. Doses included.

Show that list to your GP or pharmacist. Pharmacists are underused for this and don't require an appointment. Interaction checking is squarely what they're trained for.

If your HRT doesn't seem to be working, mention the supplements before assuming the dose is wrong. That's the specific scenario St John's wort creates, and it's the one most likely to be missed.

The honest summary

The question people search for is "what vitamins should I avoid", and the honest answer is that vitamins are rarely the issue. The risk sits with herbal preparations — St John's wort above all — and with the fact that supplement potency and safety aren't held to the standard medicines are.

That's a less dramatic answer than most pages will give you. It's the one the evidence supports.