Across the country, patients use marijuana in hopes that it will ease the symptoms of conditions such as cancer, seizures, glaucoma, and pain. Twenty states and the District of Columbia have made this use legal—including Michigan, where more than 135,000 patients are now in a four-year-old statewide registry of approved medical marijuana users.

But this wave of legalization has occurred without much independent research to support the drug’s use for these conditions, which has helped fuel the ongoing debate about such laws. And marijuana remains illegal on a federal level.

Now, with a new $2.2 million, four-year federal research grant, a team of University of Michigan Medical School researchers will try to document medical marijuana’s potential impact in a more scientific way.

The funding, from the National Institute on Drug Abuse, will pay for a two-year study of 800 Michigan patients who are seeking to obtain state certification for the use of medical marijuana for pain.

The team will approach patients who are at their first doctor’s appointment as part of the process to obtain the certification needed to become a registered medical marijuana user in Michigan. Patients may not proactively volunteer for the study; they must be approached by a member of the team in one of the participating clinics.

Each person who agrees to take part in the study will answer an array of questions at the outset, and again every six months over the course of two years.The U-M researchers will look at their symptoms, everyday functioning, and use of health care services, and other factors.

“With the ongoing policy debate and the growing popularity of medical marijuana programs in the United States, it is essential to understand the ramifications of medical marijuana use for individuals who seek access to it,” says study leader Mark Ilgen, PhD, an experienced researcher on topics related to substance use and abuse. He also is a psychologist and associate professor in the U-M Department of Psychiatry. “We hope that with this study we can help inform the debate.”

“Marijuana is the most frequently used drug in the nation, and has been legalized for medical use in many ways, yet we have very little understanding of how individuals using medical marijuana do over time,” says Frederic Blow, PhD, a co-investigator on the study and experienced substance abuse researcher who directs the Mental Health Services Outcomes & Translation Section at the U-M Medical School. “We hope this study will help provide much-needed data on the characteristics of those who seek medical marijuana, and the longer-term impact on their health and lives.”