A non-profit group of over 150 current and former athletes is calling for marijuana to be removed form the World Anti-Doping Agency's prohibited substances list.

Medical marijuana legalization is spreading across the US, but most pro-athletes are still prevented from accessing it. That's because most major sports leagues follow drug guidelines set by the World Anti-Doping Agency (WADA), which bans athletes from using cannabis even outside of competition. Players can receive suspensions if caught using cannabis.

Now athletes are pushing back for the safe of their health. And they're coming equipped with studies that suggest cannabis is a safer, more effective and less addictive pain medication than the opioids most commonly prescribed to athletes.

On Thursday, Athletes for CARE - an advocacy group that counts the likes of boxing legend Mike Tyson and NHL enforcer Riley Cote among its members - sent WADA a letter calling for cannabis to be removed from the banned substances list.

"We have found an improved quality of life through cannabis and natural cannabinoids, including significant therapeutic and wellness benefits, and these positives should be freely available to all other athletes," reads the Athletes for CARE letter sent to the WADA team developing the 2021 banned list.

"In keeping with WADA's values of ethics, fair play and honesty, the organization owes it to athletes to allow full access to this gentle but effective plant medicine."

For their part, WADA seems at least open to the idea of one day allowing athletes to use cannabis.

"It is important to note that the list is not static but evolves based on new scientific evidence, as well as, to a lesser degree, changes of use and cultural elements," WADA spokesperson James Fitzgerald told USA TODAY Sports. "Therefore, WADA maintains dialogue with athletes, administrators, scientific experts and other stakeholders and closely follows the literature in this area to obtain new evidence and information as it becomes available."

Still, WADA maintained that growing popularity and legality of cannabis would not be enough to have its classification as a banned substance changed.

Not all forms of cannabis are currently banned by WADA, however. In 2018, WADA began allowing athletes to use the non-intoxicating cannabis compound CBD, which is most often used to reduce stress, relieve pain and suppress seizures. However, THC - the compound in cannabis that gets you high - continues to be prohibited despite growing evidence that it may be a much more effective painkiller than CBD.

In addition to their letter, Athletes for CARE has also set up a petition on Change.org and is calling on both athletes and sports fans to add their voices to the groups call for athlete's access to safe, effective medical marijuana.