In what can best be described as a form of medical marijuana, new research shows that cannabis use may effectively prevent internal parasites.

At least, for Aka hunter-gatherers in the Congo basin, a team from Washington State University (WSU) reported in the American Journal of Human Biology. Evidence shows that these "pygmy" foragers, who are isolated from the cultural and media influences of Western civilization, might use plant toxins medicinally.

"In the same way we have a taste for salt, we might have a taste for psychoactive plant toxins, because these things kill parasites," Ed Hagen, a WSU Vancouver anthropologist, said in a press release.

In previous research, Hagen found that the heavier tobacco smokers among the Aka also had fewer helminths, or parasitic intestinal worms.

The researchers are unsure when the Aka might have first smoked cannabis or when it arrived on the continent. It may have come with traders from the Indian subcontinent around the first century AD, but Hagen and his colleagues say it might not have been smoked until European colonization in the 17th century.

The research team surveyed nearly all 400 adult Aka living along the Lobaye River in the Central African Republic and found roughly 70 percent of the men and six percent of the women used cannabis.

This supported evidence obtained from bioassays of the men, which found high levels of THCA in their blood. This metabolic byproduct of cannabis's active ingredient indicated that 68 percent of Aka men had recently smoked.

To find out how this recreational use might be linked to internal parasites, the researchers also collected stool samples from the hunter-gatherer population. It turns out 95 percent of men were infected with helminths, but those who consumed cannabis had a significantly lower rate of infection.

A year after being treated with a commercial antihelmintic, the cannabis users were reinfected with fewer worms.

While the Aka deliberately consume a tea of a local plant, motunga, to fight parasitic infections, they do not think of cannabis or tobacco as medicine, researchers say. This suggests they may unconsciously be, in effect, smoking medical marijuana to ward off parasites.

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