Marijuana has been used for quite some time now to treat cancer patients who live in medical marijuana states. For the most part, however, it’s only been used to treat patients who are experiencing side effects of their cancer treatment, such as the nausea and loss of appetite that comes with chemotherapy. But there is also evidence that marijuana actually cures cancer. Now, a new study from the University of East Anglia in the UK has discovered the exact compounds in marijuana that slow tumor growth.

Previous studies have found that the active ingredient in marijuana, tetrahydrocannabinol (THC), is responsible in some sort of way for slowing tumor growth. A study from 2007 found that THC targets the CB1 and CB2 cannabinoid receptors in the body — the body also produces its own cannabinoids, to an extent — and subsequently inhibits a protein responsible for aggressive cell growth. Other studies, such as this one on breast cancer, have also found that THC activates the CB2 receptor. The current study found similar results with regards to slowing tumor growth.

“We show that these effects are mediated via the joint interaction of CB2 and GPR55 — two members of the cannabinoid receptor family,” said Dr. Peter McCormick, from the university’s School of Pharmacy, in a press release. “Our findings help explain some of the well-known but still poorly understood effects of THC at low and high doses on tumor growth.”

The researchers discovered this effect after growing breast cancer tumors in mice, and then administering various doses of THC extract. But, perhaps because medical cannabis is impossible to come by in the UK, they warned about self-medicating. “Our research uses an isolated chemical compound and using the correct concentration is vital,” McCormick said in the release. “Cancer patients should not self-medicate, but I hope that our research will lead to a safe synthetic equivalent being available in the future.”

In the U.S., however, medical marijuana is abundant, with New York State recently becoming the 23rd state to legalize it. While there are obvious concerns related to using marijuana, the fact that using it medically has been picking up steam suggests that it’s working. Although actual stories of medical marijuana patients fighting cancer are few and far between, it’s possible to see the beneficial effects of the drug on patients with other diseases, such as cerebral palsy. Though there’s no hard data on the number of medical marijuana patients in the U.S., ProCon.org gives a rough estimate, putting that figure at somewhere around 2.4 million people.

Source: Moreno E, Andradas C, Medrano M, et al. Targeting CB2-GPR55 Receptor Heteromers Modulates Cancer Cell Signaling. The Journal of Biochemical Chemistry. 2014.