Trifolium pratense (red clover) is a species of clover, native to Europe, Western Asia and northwest Africa, but planted and naturalised in many other regions. It is an herbaceous, short-lived perennial plant, variable in size, growing to 20–80 cm tall. The leaves are alternate, trifoliate (with three leaflets), each leaflet 15–30 mm long and 8–15 mm broad, green with a characteristic pale crescent in the outer half of the leaf; the petiole is 1–4 cm long, with two basal stipules. The flowers are dark pink with a paler base, 12–15 mm long, produced in a dense inflorescence.
It is widely grown as a fodder crop, valued for its nitrogen fixation, which increases soil fertility. For these reasons it is used as a green manure crop. Several cultivar groups have been selected for agricultural use, mostly derived from var. sativum. It has become naturalised in many temperate areas, including the Americas and Australasia as an escape from cultivation. Red clover contains isoflavones (estrogen-like compounds) which can mimic the effect of endogenous estrogen. The use of red clover to relieve menopausal symptoms has been shown to be sometimes ineffective, but safe. The isoflavones (like irilone and pratensein) from red clover have been used to treat the symptoms of menopause. A large, well-controlled study of high-isoflavone red clover extract supplements showed a modest reduction of hot flashes with Promensil, but not Rimostil, compared to placebo. Traditionally, red clover has been administered to help restore irregular menses and to balance the acid-alkaline level of the vagina to promote conception. Red clover has been reported to be used for a variety of medicinal purposes, such as the treatment of bronchitis, burns, cancers, ulcers, sedation, asthma, and syphilis. It is an ingredient in eight-herb essiac tea.
Due to its activity on estrogen receptors, it is contraindicated in people with a history of breast cancer, endometriosis, ovarian cancer, uterine cancer, uterine fibroids, or other estrogen-sensitive conditions, but others have suggested the high isoflavone content counteracts this, and even provides benefits in these conditions. Due to its coumarin derivatives, it should be used in caution in individuals with coagulation disorders or currently undergoing anticoagulation therapy. It is metabolized by CYP3A4 and therefore caution should be used when taking it with other drugs using this metabolic pathway.
Red clover is subject to bacterial as well as fungal diseases. Other problems include parasitic nematodes (roundworms) and viruses.