As more states legalize therapeutic cannabis, some caution against overprescribing the drug, the benefits of which have not been rigorously tested in clinical trials.

 With New York State poised to become the latest inductee into the legal medical marijuana club, The New York Times explored the science behind weed’s effect on the variety of ills it’s used to treat. The paper’s verdict? Research into the medical benefits of smoked cannabis is severely lacking, and few findings point to a definitive therapeutic effect in the growing list of ailments that some physicians prescribe marijuana to treat, according to new laws. “I just don’t think the evidence is there for these long lists,” Molly Cooke, a professor of medicine at the University of California, San Francisco, told theTimes. “It’s been so hard to study marijuana. Policy makers are responding to thin data.”

As The Scientist reported in 2012, many researchers who would like to study the medical effects of smoked marijuana are stymied by nearly insurmountable obstacles to securing both research-grade supplies of the drug and funding for clinical studies. A scientist wishing to conduct a rigorous trial of smoked marijuana on a particular human disease must first register with the Drug Enforcement Administration and file an investigational new drug application with the Food and Drug Administration, among other formalities. Once all these hurdles are cleared, researchers must still win funding, which is in short supply even for less-controversial work. “It’s one thing to say we need to have more research, and it’s another thing to obstruct the research,” Steven Jenison, former medical director of New Mexico’s medical cannabis program, told the Times.

This difficulty stems in part from marijuana’s classification of an illegal, “Schedule I” drug as defined by the US Controlled Substances Act. According to that Act, the US government views cannabis—along with heroin and LSD—as a drug that has “no currently accepted medical use in treatment in the United States.”

“The [cannabis] laws date to a time when what we knew about marijuana was voodoo,” Mayo Clinic psychiatrist Michael Bostwick told The Scientist in 2012. “[The drug] can’t be applied to humans and to therapeutics because the laws don’t permit it to be done. The whole attitude towards medical marijuana is just irrational.”