Humans have used marijuana, or Cannabis sativa, for thousands of years, for religious purposes, medicinal remedies or simply getting high. These days, 1 in 8 Americans ingest or smoke marijuana, and the drug faces renewed scrutiny as more states wrestle with legalization. While the legislative battles rage on, scientists continue to study the effects this plant can have on us, therapeutic and otherwise.

But the work isn’t easy. The U.S. government hasn’t legalized marijuana and still classifies it as a Schedule I drug — with high potential for abuse, no accepted medical use and no safe use under medical supervision. To study it, experts must secure samples with a Drug Enforcement Administration stamp of approval. That makes for some serious restrictions for researchers, though they’ve made some headway.