The UK Committee on the Safety of Medicines.examined new evidence regarding the risk of interaction of St. John’s wort with a range of drugs, including warfarin, digoxin, theophylline,HIV medication and drugs used to prevent transplant
rejection. St. John’s wort induces CYPA3 enzymes, through which approximately 50% of drugs are metabolised, thus potentially reducing the half-life of cancer drugs such as indinavir and cyclosporin.47–49 Both the contraceptive Pill and
diabetic medication may be less effective and antihypertensives may be potentiated. It is possible that St. John’s wort works by inhibiting re-uptake of serotonin, dopamine and noradrenaline and by modulating interleukinF6 activity,but, as the mechanism of action remains unclear, itshould be avoided by those on monoamine oxidase inhibitors. The Department of Health has produced guidelines advising specific medical specialists, including gynaecologists, about the possible problems for patients taking St. John’swort.Blue cohosh (Caulophyllum thalictroides) is thought to increase efficiency of contractions in labour. A US study of nurse-midwives found that in those who prescribed herbs, 64% used blue cohosh and 45% used black cohosh, although 21% of these reported resulting complications such as nausea, meconium stained liquor and transient fetal tachycardia. Certain constituents appear to be vasoconstrictive and cardiotoxic and fetal
hypoxia, neonatal myocardial infarction and congestive cardiac failure have also been reported. The potential teratogenicity of anagyrine in blue cohosh is thought to require metabolism by the microflora in the rumen of
cattle, but a possible link between infant vascular and skeletal abnormalities and maternal consumption of anagyrine-containing goat’s milk has been suggested. The use by herbalists of blue cohosh has now been discontinued61 and women
should be similarly advised. Black cohosh, although more popularly used for menopausal symptoms, may be considered by some women for the promotion of efficient uterine action in labour, but others suggest that it is contraindicated in
pregnancy.The safety of echinacea prior to and during pregnancy has not been confirmed although the incidence of major embryonic malformations appears to be no greater than in non-users.Echinacea acts as an immunostimulant and is often
used prophylactically against the common cold but should be avoided in those taking immunosupressants such as corticosteroids. It has been advocated in the treatment of recurrent genitalherpes although no statistically significant benefit over placebo has been found66 Prolonged use of more than 8 weeks could lead to hepatotoxicity