Chimpanzees in East Africa may treat themselves when they feel sick using the same plants that local people use for the identical illnesses. This activity has been well documented. Richard Wrangham, Jane Goodall, and Toshisada Nishada have all recorded the feeding habits of the chimps in considerable detail.
Normally when the chimps eat, they stuff leaves into their mouths as fast as they can pull them off the branches, and then chew them rapidly. One genus of plant, however, is eaten only rarely. When eaten, it is chewed in a much different manner.
The particular genus of plant is Aspilia, a member of the sunflower family. The chimps select Aspilia leaves more cautiously. They carefully close their lips over each leaf--sometimes pausing for a few seconds--and rejecting it without pulling it off the branch. When a leaf meets with their approval, the chimp rolls the sandwich-like leaf around in its mouth and then, in a thoroughly unchimp-like manner, swallows it whole before selecting the next one.
To find out what is going on with these seldom eaten leaves, the primatologists went out looking for clues--in chimp dung. Goodall was the first to observe the phenomenon of the leaf 'pill', but wasn't sure what to make of it at the time.
The clue came when researchers found how widespread the medicinal use of Aspilia was among people. Local Tongwe people make a tea out of leaves to treat wounds, burns and other external ailments and stomach disorders, often caused by worms. Aspilia, in particular the species preferred by the local chimps, is one of the most popular African remedies.
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The leaf 'pills' were analyzed at the University of California at Irvine. They were found to contain high concentrations of a potent antibiotic called thiarubrine-A. This bright red chemical has been found in the roots of another plant of the same family in North America. Canadian Indians used to make a remedy for skin sores from these roots. This secondary metabolite is a potent antifungal and worming agent. Very low doses are effective against a variety of parasitic worms. The compound also has antiviral and antibacterial properties. It is more potent that the anti-cancer drug vincristine studied in in vitro toxicity tests.
What about other primates? Baboons do occasionally eat medicinal plants, but apparently for no particular reason other than as food. Baboons do not eat Aspilia in the chimp style.
Concentrations of the thiarubrine-A seem to follow a daily cycle. The chimps pick leaves from two of the species only around dawn, suggesting that they know that the plant will be more effective at that time of day.
Why are the leaves folded before eating? Scanning of the leaf "pills" found in dung revealed that the leaves were pockmarked with tiny ruptures, enough to release significant amounts of chemicals as they passed out through the gut. The technique was a sort of 'time release' mechanism.
Tanzanian chimps use other plants which are handled in the same manner as the Aspilia-leaf pill. The genus Lippea contains some potent compounds called monoterpenes, which are active against a range of parasites.
In summary--not only is there good evidence that chimps may self medicate, but that they are showing us potential new drugs from their very own jungle medicine chest.
..... CJ '99
Resource
Sears, C. "The Chimpanzee's Medicine Chest" New Scientist. Aug 4, 1990 pp 42-44.