Common names for Macuna pruriens include Mauritius velvet bean, Pica-Pica, Bengal bean, Cowage and Itchy bean among others. It is an annual or short-lived perennial with pubescent (hairy) leaves and seed pods that can cause extreme skin irritation. The flowers hang in elegant racemes, similar to wisteria, and are usually deep purple in colour although white varieties are available.
The vine can reach about 18 metres depending on the support, and grows best in hot, humid climates with a long, frost free growing season. Velvet bean needs to be kept moist although it will withstand short periods of drought. It is a member of the bean family Fabaceaea, and like its cousins, fixes nitrogen in the soil. For this reason, and the fact that it grows so thick and fast, it is often used as a green manure and silage for cattle. But Velvet bean has a lot more going for it than just pretty flowers and nitrogen fixing. It is a well know psychoactive drug like coffee (another common name for it in some South American countries is 'nescafe'), and one of the few natural sources of L-dopa. L-dopa is a precursor of dopamine and used to treat neurodegenerative diseases such as Parkinsons. It is also used as a testosterone booster and aphrodisiac. Besides L-dopa, Velvet bean contains serotonin and tryptamine as well as other mood influencing chemicals which are useful in treating depression and anxiety. These chemicals are contained inside the seeds which are, in their raw state, toxic. The brown, white or striped seeds are encased inside a furry seed pod (resembling a large orange or golden caterpillar) which causes a nasty, itchy reaction in most people. The variety Mucuma pruriens var. utilis is said not to cause irritation.
The pods need to be prepared carefully, boiled and the seeds soaked and boiled several times, before they can be used medicinally.