“Little is known about cannabis use in hunter-gatherers. Therefore, we investigated cannabis use in the Aka, a population of foragers of the Congo Basin.

Because cannabis contains anthelminthic compounds,” http://medical-dictionary.thefreedictionary.com/anthelmintic ” and the Aka have a high prevalence of helminthiasis, we also tested the hypothesis that cannabis use might be an unconscious form of self-medication against helminths.

THCA levels were negatively correlated with parasite infection and reinfection, supporting the self-medication hypothesis.

This, to our knowledge, is the first biomarker-validated study of cannabis use in a hunting-gathering population, and also the first to explore the relationship between the use of cannabis, which is toxic to helminths, and intestinal helminth infection.

Although the conventional view is that drug abuse impairs immunity, thus increasing susceptibility to infection, if recreational drug use is explained by the drugs’ antiparasitic properties, this would suggest that the immune system plays a key role in regulating drug use.”  

http://onlinelibrary.wiley.com/doi/10.1002/ajhb.22740/full

“Medical Marijuana Smoking Linked to Parasite Prevention. Scientists from Washington State University have suggested that smoking cannabis may have a beneficial effect with regard to the avoidance of intestinal parasite infections, which could explain why the drug has such a long history of recreational use… those who smoked cannabis had a lower rate of infection.” http://www.newhistorian.com/medical-marijuana-smoking-linked-to-parasite-prevention/3936/