Fenugreek supplements: blood sugar, breast milk and pregnancy cautions

Fenugreek seeds are familiar in curries, spice blends and as a flavouring in foods, drinks and tobacco. They have also been used medicinally for about six thousand years, as a tonic, a laxative, and for menstrual cramps, menopause symptoms, kidney stones and, in many cultures, to stimulate milk production during breastfeeding. Those traditions are the basis of today's tablets, capsules and teas.

The distinction between culinary and supplement amounts runs through every safety statement about the herb. NIH considers fenugreek safe for adults and children in the amounts commonly found in foods, and possibly safe for adults in larger amounts, but says there is not enough information to judge whether larger amounts are safe for children.

Research has suggested that fenugreek may help lower blood sugar in people with type 2 diabetes, but NIH notes that many of the studies were not of high quality, and concludes there is not enough high-quality evidence to determine whether it is useful for diabetes. That leaves a person with diabetes with a herb that might have a small effect, in an unknown amount, of uncertain consistency between products.

The practical danger is not that fenugreek replaces treatment but that it is combined with it. NIH warns that large amounts may cause a harmful drop in blood sugar. Someone taking insulin, gliclazide or another glucose-lowering medicine who adds a fenugreek supplement could therefore be at risk of hypoglycaemia, and should discuss it with their diabetes team or pharmacist before starting, and test glucose more closely if they do.

• Never stop or reduce prescribed diabetes medicine because of a supplement.

• Learn the signs of low blood sugar: shakiness, sweating, hunger, confusion, palpitations. Treat promptly and tell the team.

• Tell your diabetes team about any herbal product, including teas and spice-based tonics.

Fenugreek is probably best known to UK parents as a "galactagogue", something said to increase milk production. NIH reports that a few studies have evaluated fenugreek for milk supply in breastfeeding women with mixed results, that it is uncertain whether it can increase supply, and that more high-quality studies are needed. It also says little is known about whether larger-than-food amounts are safe while breastfeeding.

A parent worried about supply is usually better served by an infant feeding assessment than a supplement. A midwife, health visitor or breastfeeding specialist can check positioning, attachment, frequency of feeds and the baby's weight, which are far more common reasons for a low supply than any lack of a herb. Because fenugreek can also affect blood sugar, anyone with diabetes should check first.

NIH states fenugreek is not safe for use during pregnancy in amounts greater than those found in food and that its use has been linked to increased risks of birth defects in both animals and people. Supplements, concentrated teas and herbal "labour inducers" therefore belong on the avoid list for pregnancy. This matches the NHS advice to avoid herbal medicines in pregnancy.

For menstrual cramps only a small number of studies exist, the evidence is of low quality, and the effects are uncertain. Persistent, severe or worsening period pain deserves medical assessment because conditions such as endometriosis are common and treatable, and a herb should not delay that.

Possible side effects include diarrhoea, nausea and other digestive symptoms. NIH warns that fenugreek can cause allergic reactions, including serious ones, in some people. Seek urgent help (999) for facial or throat swelling, wheeze, difficulty breathing or collapse after taking it.

NIH and the NHS both point to interactions: fenugreek may interact with blood thinners and with diabetes medicines, and the NHS lists blood thinners, diabetes drugs, statins, antidepressants, blood pressure medicines and hormonal contraception among those that herbal products can affect. Ask a pharmacist, and mention fenugreek before surgery, since blood sugar and clotting are both relevant.

Fenugreek can be sold in the UK as a food or a food supplement, in which case it should not be presented as treating a disease, or as a registered herbal medicine, in which case the label shows a THR number. The MHRA says a herbal or natural ingredient does not stop a product being regulated as a medicine, and that it considers the claims made and how a product is presented. A tin of ground seed in the spice aisle is food; a capsule marketed for diabetes needs closer scrutiny.