In the battle to unlock the full medical potential of marijuana, the greatest argument against the drug is that its main psychoactive components produce unwanted side effects in tandem with its health benefits. But now researchers from Europe have isolated the tumor-shrinking pathways within cannabis, and are putting them to the test.

In a new study published in the journal PLOS Biology, researchers from the University of East Anglia, University of Barcelona, University of Pompeu Fabra, and several other European institutions are taking apart tetrahydrocannabinol, or THC, and removing the common psychoactive ingredient that commonly produces the “high.” Past research conducted by these universities, along with many other studies, has found that THC can reduce tumor growth in patients suffering from cancer.

In fact, a 2014 study found that THC, working with cannabidiol, can reduce the tumor growth of a particularly aggressive strain of brain cancer within mice. Researchers working under Dr. Wai Lui of the University of London discovered that small amounts of THC were able to shrink the brain tumor within the mice test subjects to a greater degree than prior radiation treatment. What’s more, because the necessary amounts of THC were so small, psychoactive ingredients we attribute to unwanted side effects were virtually gone.

Now, researchers are learning how to eliminate these components within THC altogether so that future medications made with cannabis only contain its cancer-killing mechanisms. When examining the various pathways within THC, researchers found that the negative cognitive effects of the component were isolated to a single pathway separate from those that shrink tumors. This pathway was found to involve both a cannabinoid receptor and a serotonin receptor, and when the serotonin receptor was blocked, THC retained its medical properties, like pain relief, without causing memory or judgment impairment.

Currently this study is also being tested on mice, but researchers remain hopeful that this new discovery will soon lead to cannabis-based therapies for human cancer patients.

“THC, the major active component of marijuana has broad medical use — including for pain relief, nausea and anxiety,” says Dr. Peter McCormick of the University of East Anglia in a recent press release. “Our previous research has also found that it could reduce tumor size in cancer patients. However, it is also known to induce numerous undesirable side effects such as memory impairment, anxiety, and dependence. There has been a great deal of medical interest in understanding the molecular mechanisms at work in THC, so that the beneficial effects can be harnessed without the side effects.”

And McCormick and his team are working hard to better understand those mechanisms, finding that when cannabinoid receptors are isolated from serotonin receptors, THC can shrink tumors without any hindering side effects. Researchers discovered that within mice, the absence of the serotonin receptor known as 5HT2AR within the brain reduced undesirable effects of THC, like memory loss. When researchers than employed a treatment to reduce 5HT2AR, THC was still able to reduce pain as well as tumor growth.

“This research is important because it identifies a way to reduce some of what, in medical treatment, are usually thought of as THC’s unwanted side effects, while maintaining several important benefits, including pain reduction,” McCormick said.

McCormick concluded by warning patients that though their study proves promising for the future of cannabis in medical settings, patients should refrain from self-medicating. He and his team are optimistic that a “safe synthetic equivalent” to current cannabis will be available for cancer patients in the near future.

Source: Scott K, Dalgleish A, Liu W. The Combination of Cannabidiol and Δ9-Tetrahydrocannabinol Enhances the Anticancer Effects of Radiation in an Orthotopic Murine Glioma Model. Molecular Cancer Therapeutics. 2014.

Moreno E, Lanfumey L, Pastor A, et al. Cognitive Impairment Induced by Delta9-tetrahydrocannabinol Occurs through Heteromers between Cannabinoid CB1 and Serotonin 5-HT2A Receptors. PLOS Biology. 2015.