In the peat swamps of Central Kalimantan, wild orangutans appear to do something long considered uniquely human: self-medicate.
A 20-year study published in Scientific Reports in mid-2026 found that Bornean orangutans consistently consume combinations of medicinal plants. These include species with antimicrobial, anti-inflammatory, and wound-healing properties. Their feeding patterns were also found to be far from random.
Around 30 percent of the 202 plant species in their diet are also recognized as medicinal by local Dayak communities.
The First Topical Treatment in Kalimantan
Evidence of this behavior had emerged long before the large-scale study was published. In 2017, a research team led by Helen Morrogh-Bernard, who later founded the Borneo Nature Foundation, documented Bornean orangutans chewing the leaves of Dracaena cantleyi without swallowing them.
Instead, the orangutans rubbed the chewed leaves onto their own arms and legs.
The same plant is used by local Indigenous communities to relieve muscle pain, joint pain, post-stroke pain, and swelling. At the time, however, the observation was regarded as an intriguing isolated case rather than evidence of a broader behavioral pattern.
A Wound That Healed Within a Week
Seven years later, further evidence emerged from a different island. In June 2022, a male Sumatran orangutan named Rakus suffered a facial wound. Researchers believe the injury was most likely caused by a fight with another male in Gunung Leuser National Park.
Three days later, researchers observed Rakus chewing the leaves of Fibraurea tinctoria. The medicinal vine has analgesic, antipyretic, and anti-inflammatory properties. It is also widely used in traditional medicine across the region to treat malaria.
Rakus did not swallow the chewed leaves. Instead, he repeatedly applied the pulp directly to his facial wound using his fingers. He continued until the wound was completely covered with the plant's juice and fibers.
Within a week, the wound had closed without any signs of infection.
A Pattern Too Consistent to Be Coincidental
The two cases raised an important question. Were these behaviors genuine self-medication, or simply isolated incidents captured by chance?
A 2026 study led by Georgia Allen, a master's student at the University of Exeter, set out to answer that question on a much larger scale. The research was conducted with Elodie Freymann, J. d'Oliveira Coelho, Kimberley Hockings, and Helen Morrogh-Bernard.
Working with Universitas Palangka Raya and CIMTROP, the team analyzed more than 20 years of behavioral records from the Orangutan Behaviour Project in the Sebangau peat swamp forest. They examined 12,236 feeding events from 55 identified orangutans, covering 202 different plant species.
To determine whether these feeding patterns were more than coincidence, the researchers applied the Self-Medicative Resource Combination Hypothesis (SMRCH). The framework proposes that non-human animals may deliberately combine therapeutic resources when ill.
They then tested the hypothesis using Multiple Distinctive Collocation Analysis (MDCA), a statistical method that measures how often two plant species appear together compared with what would be expected by chance.
The strongest pairing in the entire dataset was Mezzettia parviflora, an antioxidant-rich fruit, and Fibraurea tinctoria, the same vine Rakus used to treat his facial wound. The combination recorded a pbin value of 98.73, the highest statistical association in the dataset.
Among the 202 recorded plant species, 64 have documented ethnomedicinal uses and/or pharmacological properties. Several of these plants were not part of the orangutans' regular diet. Instead, they appeared only in specific combinations.
"Some plant species appeared together in the orangutan diet far more often than we would expect by chance," Allen wrote.
She added that the selection of these plants appears to go beyond ordinary nutritional needs. However, she also cautioned against drawing overly broad conclusions.
"At this stage, we cannot say that orangutans are consciously 'diagnosing' themselves in the same way humans would."
The researchers proposed two possible explanations that remain unresolved. The behavior may be instinctive, or it may be socially learned and passed down across generations.
A Shared Pharmacy Across Species
The findings become even more remarkable when compared with human knowledge.
Nearly one-third of the 202 plant species had already been recognized as medicinal by Dayak communities, long before researchers documented them systematically.
Fibraurea tinctoria, the plant with the strongest statistical association in the study, contains berberine. This antimicrobial and anti-inflammatory compound has long been used in traditional Southeast Asian medicine to treat malaria and jaundice.
Orangutans and humans diverged from a common ancestor millions of years ago, long before the earliest written records of medicine. Yet both species, independently, identified many of the same medicinal plants in the same forest.
