Agnus castus is an aromatic tree or shrub (Vitex agnus-castus) also known as the chaste-tree. The ancient Greeks used it to reduce libido hence the name chaste-tree; paradoxically, it has also been said historically to have aphrodisiac qualities. According to Kiple and Ornelas (2000) the berries, which resemble peppercorns and which smell and taste like pepper, have been used as a spice; its use by Christian monks is the origin of the alternative name ‘monk’s pepper’. According to Barnes (2003a) it is not used in foods, which suggests that any food use is historical or very limited.
Extracts of Agnus castus contain many substances in small amounts and it is unclear which are responsible for its biological activity. Casticin is a flavonol present in the lipophilic fraction of extracts and, since the pharmacological activity is also present in this fraction, extracts are often standardised to contain a set amount of this ingredient. To obtain the extract the crushed fruits are extracted with aqueous alcohol; 20 mg of this extract is the standard dose. Current use of Agnus castus is almost always to alleviate symptoms of the premenstrual syndrome (PMS) which may be experienced to some extent by up to 50% of young women during the luteal phase (second half) of all or some of their menstrual cycles. It is characterised by:
• A range of psychological symptoms including anxiety, aggression, irritability and depression
• Fluid retention, a bloated feeling and weight gain
• Breast tenderness.
In around 5% of women of reproductive age the symptoms may be severe enough to seriously disrupt their lives and their relationships and to meet the American Psychiatric Association’s formal diagnostic criteria (DSM-IV) for premenstrual dysphoric disorder (PMDD). The causes of these premenstrual symptoms are unclear. One suggestion that has attracted much attention in recent years is that hypersecretion of the pituitary hormone prolactin may play a role. Prolactin may cause breast tenderness and may shorten the luteal phase of the menstrual cycle leading to deficits of luteal hormones, especially progesterone. The major physiological regulator of prolactin release from the pituitary gland is the nerve transmitter dopamine, which in this context is also sometimes termed ‘prolactin inhibitory factor’. Drugs which inhibit the release of prolactin by mimicking the actions of dopamine therefore may offer potential for treating premenstrual syndrome.
Agnus castus extracts are now known to bind to dopamine receptors and to inhibit the release of prolactin in vitro, in animals and in women. Jarry et al. (1994) used an in vitro culture of rat pituitary cells to show that an active principle of Agnus castus was able to bind to dopamine receptors from these pituitary cells and to selectively inhibit prolactin release without affecting the secretion of other pituitary hormones. More recently, Meier et al. (2000) have confirmed a dopaminergic effect of Agnus castus extracts and have also suggested that it has effects upon opioid receptors that may contribute to its pharmacological actions.
There are some clinical trials in the German literature suggesting that Agnus castus may be of value in the treatment of premenstrual syndrome, and on the basis of such trials the German Commission E approved its use for this purpose. A large and well-designed study published in English has also supported the efficacy of this herb. This group used 170 women who met formal diagnostic criteria for PMS (premenstrual syndrome). They were randomly assigned to receive either a placebo or 20 mg of Agnus castus extract. Using the women’s own assessment of their condition and the physician’s global clinical impression the Agnus castus performed significantly better than the placebo. They concluded that Agnus castus is a well-tolerated and effective treatment for premenstrual syndrome.
This herb seems to be an effective and safe treatment for a specific medical condition and is approved for this use in some countries such as Germany. Given its clear pharmacological activity it would seem to be unsuitable for use as a general dietary supplement for people not suffering from this condition: it should be regarded as a herbal medicine rather than a dietary supplement. The usual dose is 20 mg of extract, which in the pharmacological grade preparation Ze440 is equivalent to 180 mg of the dried fruits. Its safety in pregnancy and lactation has not been established and it should be avoided in these conditions.