Our ancient ancestors the Neanderthals cleverly made plant-based painkillers and antibiotics to treat aches and illnesses, new University of Adelaide research has found.

A study published in the journal Nature analysed ancient DNA found in dental plaque of Neanderthals to learn more about their lifestyle, behaviour and diet.

The researchers compared samples from four Neanderthals found at the cave sites of Spy Cave in Belgium and El Sidron in Spain.

The plaque, material that forms on and between teeth, contained food particles as well as microbes from the mouth as well as respiratory and gastrointestinal tracts.

Co-author Alan Cooper from the University of Adelaide said one of the most surprising finds was that our extinct ancestors could make natural medicines.

The jawbone from an adolescent male at the Spanish site had a painful dental abscess, while plaque showed he had an intestinal parasite that caused diarrhoea.

The ancient man was clearly sick, but he was receiving treatment, Professor Cooper said.

"He was eating poplar, which contains the painkiller salicylic acid, the active ingredient of aspirin," he said.

"We could also detect a natural antibiotic mould."

Professor Cooper said it showed Neanderthals possessed a good knowledge of the medicinal properties of plants and seemed to be self-medicating.

He said the findings contrast with the views many people hold that of our ancient relatives were simplistic and unintelligent.

"This is more than 40,000 years before we developed penicillin," he said.

Co-lead author of the study paleomicrobiologist Laura Weyrich, also of the University of Adelaide, said: "This study really gives us a glimpse of what was in a Neanderthal's medicine cabinet.

"I definitely believe our research suggests Neanderthals were highly capable, intelligent, likely friendly beings. We really need to rewrite the history books about their 'caveman-like' behaviours. They were very human-like behaviours," she said.

The robust, large-browed Neanderthals prospered across Europe and Asia from about 350,000 years ago until going extinct roughly 35,000 years ago, after our species, which first appeared in Africa 200,000 years ago, established itself in regions where Neanderthals lived.

Scientists say Neanderthals were intelligent, with complex hunting methods, probable use of spoken language and symbolic objects, and sophisticated fire usage.

The researchers also reconstructed the genome of a 48,000-year-old oral bacterium from one of the Neanderthals.

"This is the oldest microbial genome to date, by about 43,000 years," Dr Weyrich said.

At Belgium's Spy Cave site, which at the time was a hilly grassy environment home to big game, the Neanderthal diet was meat-based with woolly rhinoceros and wild sheep, along with wild mushrooms. 

About 12,000 years earlier, at Spain's El Sidron Cave site, which was a densely forested environment most likely lacking large animals, the diet was wild mushrooms, pine nuts, moss and tree bark, with no sign of meat.

The two populations apparently lived different lifestyles shaped by their environments, the researchers said.

The study was a collaboration between the University of Adelaide's Centre for Ancient DNA, the university's dental school and the University of Liverpool in Britain.

AAP, Reuters