Momordica charantia (Bitter gourd, Karela - Cucurbitaceae) is a climber that grows in tropical parts of Asia, Africa, the Caribbean and South America. The plant has a long history of use as a hypoglycemic agent in the countries where they are grown. Data from in vitro, animal and human studies show its utility in the treatment of diabetes. More recently, momordica has been proposed as an antiviral and antineoplastic agent.

Extracts and powdered formulations of the fruit are most used. Less frequently, teas made from the leaves and stems of the plant are also used. Momordica is also consumed as a food stuff that is available throughout the year.

Early studies suggested that momordica has insulin-like properties. Other evidence indicate that it may decrease hepatic gluconeogenesis, increase hepatic glycogen synthesis and increase peripheral glucose oxidation in erythrocytes and adipocytes. Studies also suggest that momordica increases insulin secretion and beta cell production in the pancreas; this claim has not been proven in studies.

Although several constituents of bitter gourd have been found to have hypoglycemic properties, most interest has been centered on a polypeptide fraction. These have been variously described as polypeptide-p and polypeptide-K. A mixture of steryl glycosides, termed charantin, has also been credited with hypoglycemic properties.

In one study, 19 subjects were enrolled, 14 with either type 1 or type 2 diabetes. Five diabetic patients and five healthy volunteers received placebo. A water-soluble extract of momordica was made in a subcutaneous form containing 1.8 mg of 'vegetable insulin' per 40-unit dose. Nine of the diabetic patients were placed on a sliding scale to receive 10 units of the preparation if the fasting blood glucose concentration was less than 180 mg/dl; 20 units for 180-250 mg/dl and 30 units for >250 mg/dl. The primary end point was a decrease in fasting blood glucose, which was measured at multiple time points over 12 hours. The authors reported a mean decrease in serum glucose levels for the diabetic patients receiving momordica , with effects noted as early as 30 min ( a decrease from 21.5% from a mean baseline glucose concentration of 295 mg/dl), a maximum reduction at 4 h (49.2%) and persistent effects after 12 h (a 28% drop). In contrast, diabetic patients and healthy volunteers who received the placebo experienced a 5% drop in serum glucose levels during the study period.

In a case-series study involving 18 patients with newly diagnosed diabetes were given 100 ml of momordica fruit juice 30 min before glucose loading for a glucose-tolerance test (GTT). The results were compared with the subject's own experience to a GTT on the previous day, when water was given as a control. Thirteen (73%) patients showed significant improvements in GTT results after taking momordica. In another case-series study, 12 patients with type 2 diabetes received one of two momordica preparations: 1) an aqueous extract, prepared by boiling 100g of chopped momordica in 200 ml water until the volume was reduced to 100ml given daily as a single morning dose, and 2) 5g of dried fruit powder, consumed thrice daily. After 3 weeks, patients in the aqueous extract group, a significant 54% reduction in blood glucose level was seen. However, in the powder group, the drop was less significant at 25%.

In a recent study on the effect of an aqueous extract of momordica seeds on oxidative stress in plasma and pancreas of streptozotocin-induced diabetic rats, beneficial effects on impaired oxidative stress was noted. Oraal administration of the seed extract at a dosage of 150 mg/kg body weight for 30 days resulted in significant reduction in plasma glucose, thiobarbituric acid-reactive substances, lipid hydroperoxides and significant improvement in ascorbic acid, reduced glutathione and insulin.

A 30kDa protein containing 263 amino acids has been isolated, purified and cloned from momordica. This protein, coded MAP-30, is credited with anti-HIV and anti-tumor activities. This protein is reported to inhibit HIV viraal integrase and render them unable to integrate themselves into the host cell genomes. MAP-30 is an N-glycosidase that depurinates the adenine base of rat liver rRNA, thereby inhibiting ribosomal protein synthesis. This property is believed to be distinct from its ribosome inactivating property.