The neem tree is a tropical evergreen that's been part of traditional Asian medicine for centuries. Practitioners recommend neem leaves and other parts of the tree to treat gastrointestinal problems, to prevent infection and, when used topically, as an insect repellent and pesticide. Some studies indicate that components of neem leaves might have significant benefits when taken in supplement form, but large studies with human subjects are still needed, along with studies to confirm that eating the leaves has the same benefits.
Neem leaves contain several phytochemicals, or natural plant compounds, that have significant biological activity. These include components called flavonoids, such as quercetin, catechin, carotenes and ascorbic acid, which are antioxidants. Antioxidants help protect all your cells from the effects of unstable chemicals called free radicals that form naturally during digestion, in your skin when you're exposed to sun and in your organs when you encounter toxins such as cigarette smoke. Over time, exposure to free radicals can damage cellular DNA and other cell components, changes that the Linus Pauling Institute reports might raise your risk of disorders such as atherosclerosis and neurological diseases; these changes could also speed the aging process.
Experts at the Memorial Sloan Kettering Cancer Center report that extracts made from neem leaves might have significant anti-cancer properties, helping prevent or slow growth of several types of cancer cells in cultures and laboratory animals. A study published in the November 2012 issue of Archives of Gynecology and Obstetrics found that neem-treated cervical cancer cells died at a higher rate than untreated cells, while another study in the April 2006 issue of the Journal of Ethnopharmacology reported that a neem extract had a similar anti-growth effect on prostate cancer cells. Research published in the September 2002 issue of Phytotherapy Research found that neem leaf extract protected laboratory animals exposed to a carcinogen from changes that signal growth of stomach cancer, compared to controls, but these findings still need confirmation in clinical studies with human subjects.
The cancer center also reports that neem leaves have antimicrobial properties, potentially helping prevent or slow growth of pathogens. For example, neem leaf extract might help prevent growth of viruses such as the HIV virus, according to a paper in the July 2004 issue of Transactions of the Royal Society of Tropical Medicine and Hygiene. The study found that 10 subjects who were HIV-positive and took neem-containing capsules for 30 days gained weight and had higher numbers of immune cells in their blood, which the authors attributed to reduced growth of the HIV virus. An oral gel made from neem leaves also helped lower levels of several types of bacteria in the mouths of human subjects, compared to controls, according to a study in the January 2004 issue of the Journal of Ethnopharmacology. But both studies were small and, although results are promising, the antimicrobial activity of neem still needs further study.
Fresh neem leaves may be available at some specialty stores or in catalogs, but no research is available on possible benefits of eating fresh leaves. Extracts made from leaves that are similar to those used in research studies are available from health-food stores in capsules or tablets. Although neem supplements are considered safe and without significant adverse effects, no minimum effective dose has been identified as of 2015. Neem might cause itching or other problems in people allergic to the tree, and you should avoid taking neem leaves if you're pregnant or breast-feeding because its safety during these times hasn't been established. Talk to your doctor about using neem leaves to decide if they might be helpful in your situation.