Wild animals sometimes act as their own doctors. Scientists call this zoopharmacognosy, and evidence for it has been building for years. Chimpanzees swallow rough leaves whole to flush parasites out of their intestines. Bonobos, gibbons, and gorillas show similar practices.
However, orangutans have consistently slipped under researchers’ radar. A new study suggests they still deserve a place in this narrative and that they might be doing something more complex than their relatives. The findings were published in the journal Scientific Reports.
For a long time, orangutans were considered an exception among great apes. They were the only ones never documented swallowing whole leaves to get rid of worms.
But several clues pointed to the contrary. On Borneo, females were seen chewing leaves from Dracaena cantleyi and rubbing the foam onto inflamed limbs—a plant that local people use for the same purpose.
Then, in 2024, a male orangutan was filmed on Sumatra pressing chewed leaves from a medicinal plant against a fresh wound on his face. These were striking moments, but they were isolated observations of individual plants.
Researchers needed more reliable data than single sightings. They turned to one of the largest existing datasets on orangutans. Field teams in the peat swamp forest of Sebangau in Central Kalimantan, Indonesia, had been tracking these apes since 2003.
The study gathered data on 55 individual orangutans over 2419 days and more than 12,000 separate feeding events. In total, the orangutans fed on 202 plant species. This broad overview allowed the team to ask a question that couldn’t be addressed with isolated observations.
Most studies on self-medication have focused on one plant at a time. The new work, by contrast, borrowed a fresh idea. The research team applied the Self-Medication Resource Combination Hypothesis (SMRCH), which suggests that animals may combine medicinal plants rather than relying on a single remedy. Two plants taken together could be more effective than each one alone.
The researchers looked for plant combinations that occurred far more often than random chance would allow. They matched the orangutans’ diet with plants that Dayak communities living near the forest use as medicine.
Thus, out of 64 species with confirmed medicinal value, 19 of the most promising candidates were selected for closer study.
When patterns emerged, one plant kept showing up again and again. A climbing vine called Fibraurea tinctoria appeared in nearly three-quarters of the strongest non-random pairings. Its tightest partnership was with fruits from Mezzettia parviflora, and this combination stood out as the most striking association across the entire dataset.
Historical sources also repeatedly mentioned this plant paired with leaves, fruits, and even termites. These were not random bites. The same individuals came back in a specific sequence far more often than normal feeding could explain.
The chemical makeup of these plants is highly telling. Fibraurea tinctoria contains berberine, a compound with antimicrobial and anti-inflammatory effects. Traditional healers in some parts of Southeast Asia have used Fibraurea tinctoria to treat conditions like malaria and jaundice.
Species from the genus Alyxia show anti-inflammatory and antimicrobial activity. Species from the genus Willughbeia affect enzymes linked to memory. Additionally, Mezzettia parviflora is a rich source of antioxidants. As the researchers note, together these plants could provide anti-inflammatory, antimicrobial, and wound-healing effects simultaneously.
The clearest sign of orangutans’ purposefulness lies in what they didn’t do. Many of these medicinal plants are not part of their main diet.
The research was led as part of her master’s thesis in conservation and biodiversity.
“What’s interesting about these findings is that some plant species appeared together in the orangutans’ diet much more often than you’d expect by chance,” explains Georgia Allen from the University of Exeter. “We know some of these plants contain compounds with antimicrobial, anti-inflammatory, or wound-healing properties. Importantly, many of these plants don’t make up a significant part of the orangutans’ overall diet, suggesting they’re consumed for specific benefits rather than as everyday food.”
The study leans heavily on knowledge passed down over many generations. Many of the plants the orangutans chose are the same ones Dayak people turn to when they get sick. Staff who led the fieldwork have spent over a decade learning local names, plant parts used, and the illnesses they treat.
The overlap between ape and human medicine kits partly explains how convincing the results are. It also points to broader relevance in this work. The authors argue that protecting indigenous knowledge is important for preserving biodiversity and for global health research.
Researchers carefully weigh how far they can push their claims. Statistical patterns are not proof of intention.
“At this stage, we can’t say that orangutans consciously ‘diagnose’ themselves the way humans do,” says Allen. “But our findings show they selectively consume certain plants with medicinal properties, and this consumption goes beyond simple feeding.”
Exactly how the apes might learn this remains unclear. The group suggests it’s a mix of instinct and behavioral traits passed down through generations, though plant availability and habitat may also influence some patterns.
The real potential may lie in the approach itself. Collecting health data on wild apes is almost impossible, which has long held back this field. Instead, by analyzing decades of feeding data, this method allows researchers to identify promising plants without waiting to catch a sick animal in the act.
The next step is to test whether these combinations truly work better together in a lab setting. For now, the forest has given scientists a new list of leads and reminded us that we may have been underestimating orangutans all along.
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