Chimpanzees May Self-Medicate With Plants, Using the Forest as a Pharmacy

Chimpanzees may be using the forest like their own personal pharmacy. When they’re sick, the primates appear to seek out and eat plants with antibacterial and anti-inflammatory properties, according to new research.

Observers have long suspected that chimpanzees use plants to self-medicate. Now, a new paper published last week in the journal PLOS ONE offers more evidence in support of this idea.

Researchers followed two groups of wild chimpanzees through Uganda’s Budongo Forest for eight months. They recorded what the animals ate, as well as whether they were sick—which they determined by checking their feces for parasites, testing their urine for elevated levels of immune cells and looking for wounds.

The team then studied samples of 13 plant species the sick chimps had eaten. Though the plants provided very little nutritional value to the animals, they did have medicinal benefits. By analyzing extracts from the plants, scientists determined 88 percent inhibited the growth of bacteria—including some known to cause illness in humans—and 33 percent displayed anti-inflammatory activity.

In one case, a chimp with diarrhea and tapeworms traveled away from his group’s usual home to a spot in the forest with lots of Alstonia boonei trees. He gathered up some of the trees’ dead wood, then munched on it. When the scientists tested the dead wood, they found “high levels of antibacterial and anti-inflammatory activity in the extracts of this species,” they write in the paper.

Another chimp was seen limping, because one of his hands was badly injured. He moved a few meters away from his group to search for and eat a type of fern called Christella parasitica. It was only the second time anyone had recorded a chimp eating this type of plant in 30 years of study. Later, when the researchers tested the fern, they found it “produced notably high anti-inflammatory activity,” which may have helped reduce swelling and pain in the chimp’s hand, they write.

NEW PAPER OUT! In our new study in @PLOSONE, we combined behavioral observations with pharmacological testing to highlight several plant species as suspect medicinal resources for the wild chimpanzees of the Budongo Forest. More info below: https://t.co/9yGuohSaz8

— Elodie Freymann (PhD) (@ElodieFreymann) June 21, 2024

The findings are not definitive proof that chimps are self-medicating, but they offer “strong support” for the behavior, the researchers write. The results also add to the growing body of knowledge about chimpanzees, which split from humans on the evolutionary tree roughly 6 million to 8 million years ago.

“It’s always very fascinating to find out that our closest relatives are showing behaviors that we humans also show,” says Isabelle Laumer, a primatologist and cognitive biologist at the Max Planck Institute of Animal Behavior who was not involved with the research, to the Washington Post’s Frances Vinall.

The chimpanzee observations might also aid the discovery of new medicines for humans—or, at the very least, help narrow down the search.

“We can’t test [every plant] in these forests for their medicinal properties,” says study lead author Elodie Freymann, a primatologist at the University of Oxford in England, to BBC News’ Victoria Gill. “So why not test the plants that we have this information about—plants the chimps are seeking out?”

It’s not clear how chimpanzees learn which plants might help make them feel better. But they “may have used the same trial and observation methods humans have used to find effective medicines, then passed on the information to their offspring,” says John Arnason, a phytochemist and ethnopharmacologist at the University of Ottawa who was not involved with the study, to Science’s Dennis Normile.

Chimpanzees are not the only non-human animals that may use medicine. In June 2022, researchers observed a Sumatran orangutan treating his own injury with a medicinal plant called yellow root. He not only ate the stems and leaves—he spread the juices and poultice on his wound, too.

Dolphins have also been seen rubbing against corals and sea sponges, which have antibacterial and antimicrobial properties. They may be using the invertebrates to fend off skin infections, research suggests. Brown bears may scratch their backs on trees with antifungal and antiparasitic properties to repel ticks, while great bustards consume plants that could combat sexually transmitted infections.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.