Medical marijuana is still a relatively new phenomenon, although the early results are looking good, with a recent study indicating that opioid painkiller use is noticeably down in states that allow doctors to prescribe cannabis. The paper, which appears in the journal Health Affairs, provides some hard evidence that people in these states are indeed using medical marijuana for its intended purpose, rather than just recreationally, as some had initially feared.

Researchers reviewed prescriptions filled by Medicare enrollees across the US from 2010 to 2013, looking particularly at prescription rates for medications for which marijuana can serve as a clinical alternative. Towards the end of this timescale, data showed that the average physician in states that permitted medical marijuana was prescribing 1,826 fewer doses of pharmaceutical painkillers per year than those in states that did not allow the clinical use of cannabis.

Doctors in these states also prescribed 562 fewer doses of anti-anxiety drugs, 541 fewer doses of anti-nausea medication, and 486 fewer doses of pharmaceuticals designed to treat seizures than doctors in other states. According to the study authors, this indicates that many people were using medical marijuana as an alternative to these medications by 2013.

At that point, 17 US states, as well as the District of Columbia, had passed laws allowing the use of the drug. Across these locations, the amount of money saved by Medicare programs as a result of this reduction in prescriptions was $165.2 million. The researchers estimate that if all states had permitted the medical use of marijuana at this time, the total saving would have been $468 million.

In a statement, study co-author Ashley Bradford explained that “the results suggest people are really using marijuana as medicine and just using it for recreational purposes,” which is good news given that the number of states allowing the clinical use of the drug has since risen to 24.

Opioid addiction is a growing health concern in the US, with many people becoming hooked on prescription painkillers. Earlier this year, the scale of the problem was likened to an “epidemic” in the wake of a sharp rise in overdose deaths. The substitution of these highly addictive medications for marijuana could therefore help to curb this alarming trend.