Agnus castus (Vitex agnus-castus), also known as Chaste tree and Monk’s pepper, grows in Mediterranean countries and central Asia. The dried fruit, which has a pepper-like aroma and flavour, is used in herbal medicine preparations.

The common name of this pretty herb is Chaste Tree, harking back to the Crusaders’ belief that it would crush their wives’ libidos whilst they were off crusading. Whether it actually achieved this effect is doubtful as it is now recognised as boosting female fertility and easing menstrual symptoms, but the wives obviously weren’t telling and who can blame them? Athenian women used to put the leaves in their beds to help with gynaecological problems, which also sounds rather dubious! Monks, however, used to grind the seeds to make pepper, which was believed to help keep them ‘chaste’, and this is rather more credible as we now use Agnus castus for teenage acne in boys, so it may well balance testosterone levels in men.

The benefits of Agnus castus come from its actions upon the pituitary gland – specifically on the production of a hormone called luteinising hormone (LH), which indirectly increases progesterone production and helps regulate the menstrual cycle. Agnus castus also keeps prolactin secretion in check, which may benefit some infertile women as well as some women with breast tenderness associated with premenstrual syndrome (PMS).

A trial published in the British Medical Journal in 2001 showed Agnus castus to have a beneficial effect on PMS symptoms, ranging from anger and irritability to bloating and breast fullness. The herb was well tolerated and did not cause unwanted side effects.

Another trial published in 2000, showed 42% of the 1,634 women involved reporting that they no longer suffered from PMS! Overall, 93% of the women on the trial reported that their PMS symptoms either disappeared or decreased. Interestingly, 23 of the women on the trial fell pregnant whilst taking Agnus castus and 19 of them had previously had fertility problems. Seemingly, not only does Agnus castus increase progesterone, but it inhibits prolactin high levels of which have been connected to infertility It is therefore well worth trying if you’ve had problems conceiving.

A controlled clinical trial found that women taking 20 mg per day of a concentrated Agnus castus extract for three menstrual cycles had a significant reduction in symptoms of PMS, including irritability, mood swings, headache and breast tenderness. A review of other trials and case reports suggests there is at least preliminary support that Agnus castus should be considered for women with irregular periods, infertility and mildly elevated prolactin levels.

How is it usually taken?

As the dried herb in capsules or as in liquid preparations. Agnus castus is typically taken once in the morning with liquid for several months consecutively.

With its emphasis on long-term balancing of a woman’s hormonal system, Agnus castus is not a fast-acting herb and is unlikely to give immediate relief to the discomfort associated with PMS. For premenstrual syndrome, or frequent or heavy periods, Agnus castus can be used continuously for four to six months. Infertile women with amenorrhoea (lack of menstruation) can remain on Agnus castus for 12 to 18 months, unless pregnancy occurs during treatment.

Are there any side effects or interactions?

Side effects may include minor stomach upset and a mild skin rash with itching. Agnus castus is not recommended for use during pregnancy and should not be used concurrently with hormone therapy (e.g., oestrogen, progesterone).