Bitter melon has been used in various Asian traditional medicine systems for a long time. Like most bitter-tasting foods, bitter melon stimulates digestion. While this can be helpful in people with sluggish digestion, dyspepsia, and constipation, it can sometimes make heartburn and ulcers worse. The fact that bitter melon is also a demulcent and at least mild inflammation modulator, however, means that it rarely does have these negative effects, based on clinical experience and traditional reports.

Though it has been claimed that bitter melon's bitterness comes from quinine, no evidence supports this claim. Bitter melon is traditionally regarded by Asians, as well as Panamanians and Colombians, as useful for preventing and treating malaria. Laboratory studies have confirmed that various species of bitter melon have anti-malarial activity, though human studies have not yet been published.

In Panama bitter melon is known as Balsamino. The pods are smaller and bright orange when ripe with very sweet red seeds, but only the leaves of the plant are brewed in hot water to create a tea to treat malaria and diabetes. The leaves are allowed to steep in hot water before being strained thoroughly so that only the remaining liquid is used for the tea.

Laboratory tests suggest that compounds in bitter melon might be effective for treating HIV infection. As most compounds isolated from bitter melon that impact HIV have either been proteins or glycoproteins lectins, neither of which are well-absorbed, it is unlikely that oral intake of bitter melon will slow HIV in infected people. It is possible oral ingestion of bitter melon could offset negative effects of anti-HIV drugs, if a test tube study can be shown to be applicable to people. In one preliminary clinical trial, an enema form of a bitter melon extract showed some benefits in people infected with HIV (Zhang 1992). Clearly more research is necessary before this could be recommended.

The other realm showing the most promise related to bitter melon is as an immunomodulator. One clinical trial found very limited evidence that bitter melon might improve immune cell function in people with cancer, but this needs to be verified and amplified in other research. If proven correct this is another way bitter melon could help people infected with HIV.

Folk wisdom has it that bitter melon helps to prevent or counteract type-II diabetes. A recent scientific study at the Jawaharlal Institute of Postgraduate Medical Education and Research, India, has proved that bitter melon increases insulin sensitivity. Also, in 2007, the Philippine Department of Health issued a circular stating that bitter melon, as a scientifically validated herbal medicinal plant, can lower elevated blood sugar levels. The study revealed that a 100 milligram per kilo dose per day is comparable to 2.5 milligrams of the anti-diabetes drug Glibenclamide taken twice per day. Bitter melon is sold in the Philippines as a food supplement and marketed under the trade name Charantia. Charantia capsules and tea are being exported to the United States, Canada, Europe, Mexico, Japan, Korea, and parts of the Middle East.

Bitter Melon contains four very promising bioactive compounds. These compounds activate a protein called AMPK, which is well known for regulating fuel metabolism and enabling glucose uptake, processes which are impaired in diabetics. "We can now understand at a molecular level why bitter melon works as a treatment for diabetes," said David James, director of the diabetes and obesity program at the Garvan Institute of Medical Research in Sydney. "By isolating the compounds we believe to be therapeutic, we can investigate how they work together in our cells." 

Bitter melon contains a lectin that has insulin-like activity. The insulin-like bioactivity of this lectin is due to its linking together 2 insulin receptors. This lectin lowers blood glucose concentrations by acting on peripheral tissues and, similar to insulin's effects in the brain, suppressing appetite. This lectin is likely a major contributor to the hypoglycemic effect that develops after eating bitter melon and why it may be a way of managing adult-onset diabetes. Lectin binding is non-protein specific, and this is likely why bitter melon has been credited with immunostimulatory activity - by linking receptors that modulate the immune system, thereby stimulating said receptors.

On the other hand, bitter melon seed contains an insulin like protein called polypeptide-k. Polypeptide-k helps in lowering blood glucose level by acting as insulin, rejuvenating beta cells of pancreas and activate inactive insulin (insulin resistance). Polypeptide-k is marketed in Malaysia under the trade name of Diabegard.

Various cautions are indicated. The seeds contains vicine and therefore can trigger symptoms of favism in susceptible individuals. In addition, the red arils of the seeds are reported to be toxic to children, and the fruit is contraindicated during pregnancy.