But the idea that marijuana improves performance is not supported by science. To the contrary, the evidence is inconclusive at best, while an overview of the research concludes that marijuana hinders performance by reducing stamina and peak performance while increasing heart and breathing rate. A close examination of the scientific literature reveals an additional wrinkle: In justifying its ban on the drug, WADA, which sets the policy for drug prohibition, has overstated anecdotal and speculative evidence, experts said. In 2011, two WADA scientists and an adviser wrote a paper that is widely cited as representing WADA’s argument that marijuana should be prohibited because it can enhance performance. But some experts question the paper’s accuracy. “The ‘evidence’ is extraordinarily weak, at least as far as this paper goes,” said Margaret Haney, a professor of neurobiology at Columbia University, where she is director of the Cannabis Research Laboratory. Dr. Haney said that the broader body of research — going beyond the crucial 2011 paper — also didn’t support the claims. Marijuana, she said, “reduces reaction time and has other effects that would worsen performance.”