Medicines, foods and supplements to avoid on letrozole

Letrozole has fewer interactions than many cancer medicines, but a few things matter. The most important are products that contain oestrogen, because letrozole works by lowering oestrogen and adding it back works against the treatment. These include hormone replacement therapy, the combined contraceptive pill, some menopause remedies and, in most cases, vaginal oestrogen creams, tablets or rings unless your oncologist has agreed to them. Tamoxifen is not taken at the same time as letrozole, because it lowers letrozole levels in the blood and the combination has not shown extra benefit. Some herbal products are also a concern. St John's wort speeds up the liver enzymes that break down many medicines and may lower letrozole levels, and concentrated plant oestrogen supplements, such as soy isoflavone capsules or red clover, could in theory counteract the tablet. On the other hand, most everyday medicines are fine with letrozole, including paracetamol, common blood pressure and diabetes tablets, calcium and vitamin D, and bone-strengthening medicines. There are no special food rules. A normal diet with soy foods such as tofu or soya chunks in usual amounts is generally considered safe, and grapefruit is not known to matter for letrozole, unlike some other cancer tablets. Alcohol is best kept low for general and bone health. Because product labels change and combinations differ, always tell every doctor, dentist and pharmacist that you take letrozole, and check before starting anything new.

Oestrogen is the main thing to avoid

Hormone replacement therapy and oestrogen-containing products can undo letrozole's effect.

Check herbal products

St John's wort and plant oestrogen supplements are the herbs most often flagged.

Most daily medicines are fine

Everyday tablets for blood pressure, diabetes, pain and bones rarely cause problems.

Advice about interactions is often based on how medicines are broken down, rather than on large studies of people.

Much of the evidence is indirect

Many warnings come from laboratory findings or single reports. The real effect in people may be smaller or larger.

Herbal products are hard to judge

Strength and ingredients vary between brands and batches, and labels do not always list everything.

Food fears are often overstated

Normal Indian meals, including dal, soy and spices, are not known to interfere with letrozole. The concern is mainly with concentrated supplements.

What this page cannot tell you

It cannot check your personal medicine list. Your pharmacist or oncologist can.

Letrozole rarely needs to be stopped for other treatment, but everyone caring for you should know you take it.

Dentists

Letrozole itself does not affect dental work. If you also have bone medicines such as zoledronic acid or denosumab, your dentist needs to know before extractions or implants.

Surgery

Most surgeons let you continue letrozole around operations. Confirm this with your surgical team.

New prescriptions

Show your medicine list to any new doctor, and ask the pharmacist to check each new product.