This story is part of a partnership between MedPage Today and VICE News.

It used to be normal to find Navy veteran Shane O'Neil sitting in his basement, snorting Adderall and washing down opioids with alcohol to deal with post traumatic stress disorder and other injuries sustained in the line of duty. And it was legal because he got the drugs from the VA hospital.

Okay, maybe snorting wasn't on the prescription pad. But the former "full-blown pill addict" says the only illegal substance he put in his body was the one that saved his life: Marijuana.

"I had a friend take a shotgun out of my mouth in 2014," said O'Neil, 36, referring to the time before he replaced his pills with cannabis. "And now it's like I have a new life, literally. We take our kids to karate, out to dinner. I'm home, not out until 3am chasing drugs, drinking, and hiding from people."

Medical marijuana isn't legal where O'Neil lives with his wife and their four children in Ohio, and even if it was, PTSD is not a qualifying condition to get medical cannabis in most states.

Colorado, for example, rejected PTSD as a qualifying condition for medical marijuana because there wasn't enough research to support it. Dr. Margaret Gedde, a Colorado doctor who's treated more than 2,000 medical marijuana patients a year since 2009, said this a problem even though anyone in her state can can get recreational marijuana. Recreational marijuana is taxed more heavily than medical marijuana, and the staff at recreational marijuana retailers aren't as knowledgeable about cannabis for medical conditions, she said.

Dr. Sue Sisley, formerly of the University of Arizona, has been trying to get her cannabis for PTSD trial off the ground for years, but she says the main problem is that researchers like her can only legally get cannabis from one source: The University of Mississippi, which is under contract with the National Institute on Drug Abuse (NIDA) to grow cannabis for studies. But Sisley says the university hasn't been able to grow the strains she's requested, and she thinks the "monopoly" has to end.

"It's really the final hurdle that continues to impede cannabis research in this country," Sisley said.

The "monopoly" is the result of an international agreement that took place in 1961, called the Single Convention on Narcotic Drugs, which laid the groundwork for the US to designate cannabis as a Schedule I drug, like heroin, meaning the strictest rules apply because it is considered one of the most dangerous substances. Under the Controlled Substances Act of 1970, which put these rules into effect, the Drug Enforcement Administration (DEA) was put in charge of licensing organizations to grow cannabis for research.

To date, the DEA has only licensed the University of Mississippi to do grow pot for research purposes. Another a grower at the University of Massachusetts-Amherst applied for a license more than a decade ago, but the request was denied.

Sisley said she's asked Ole Miss for cannabis that was 12 percent tetrahydrocannabinol (THC), which is the psychoactive chemical in marijuana, and 12 percent cannabidiol (CBD), which is a non psychoactive part of the plant that has been used to treat epilepsy in recent years. But Sisley said the best they could offer was 7 percent THC and 7 percent CBD.

'We're trying to do a real world study and imitate what veterans do everyday. I feel like this sabotages an efficacy study from the beginning.'

"We're trying to do a real world study and imitate what veterans do everyday," she said, adding that veterans can get products with up to 28 percent THC in dispensaries or on the streets. "I feel like this sabotages an efficacy study from the beginning."

Steven Gust, PhD, who directs NIDA's international program, said Sisley's experience was a unique one.

NIDA, together with Ole Miss, grants between 20 and 30 requests for medical marijuana for studies each year, Gust said, and that's stayed roughly the same for between five and 10 years.

Don Abrams, an oncologist at the University of California San Francisco, said the University of Mississippi and NIDA have been very responsive to his requests for various strains over the years.

"It's there if you ask for it, they'll provide it," Abrams said. "There are people who take issue with fact that he [Mahmoud ElSohly at the University of Mississippi] has a monopoly, but don't think that should be the case."

Gust said he's been at NIDA for 20 years, and only a handful of people have been denied access to medical marijuana for studies, but NIDA isn't the agency that denies them. Anyone who has been given the go-ahead by the DEA and the Food and Drug Administration to obtain medical marijuana for a specific study can do so, he said.

Since about 2014, researchers have been more interested in cannabis high in CBD, Gust said.

"We have a pretty wide range of THC and CBD ratios available for the research community," he said.

Currently, marijuana available to researchers is between 2 percent and 6.7 percent THC and .02 percent and .08 percent CBD, according to NIDA. However, according to the website for The Clinic, which has six medical marijuana dispensaries in Colorado, one in Illinois and a pending location in Nevada, a marijuana strain called "cherry pie" has 19.6 percent THC. Another strain called "pre '98 bubba kush" has 8.82 percent THC and 15.63 CBD.

NIDA will soon only make marijuana orders available in bulk, and says it considers high THC to be above 10 percent.

Still, there are other components of marijuana, like terpenes, that haven't been well studied, but would require more plant strains to do so, said Gust. However, it would be "very, very difficult, almost impossible" for NIDA to replicate these strains because they're grown in various places and conditions, which would make the endeavor expensive and time consuming.

"It makes a lot of sense," he said, referring to the study of terpenes and other marijuana components in general. "NIDA would support that wholeheartedly and wishes we had a way to do that."

The Multidisciplinary Association for Psychedelic Studies (MAPS) has received a $2.1 million grant to fund Sisley's PTSD study, part of which will take place at Johns Hopkins University Hospital. Now that the DEA will review marijuana's status as a Schedule I drug this year, and potentially loosen restrictions on research as well, MAPS plans to resubmit the UMass marijuana farm application and hopefully start a marijuana farm of its own.

When asked about what he predicts for the future of medical marijuana research, Gust said he expected a significant increase in medical cannabis studies after 1999, when a review of the harms and potential benefits of marijuana were published in a medical journal, and the authors called for more research.

"We haven't seen a large increase in interest over those ensuing years," he said. "People will say that's because of the Schedule I status of marijuana, which certainly doesn't help, but it's not an insurmountable barrier."

Watch the VICE News documentary Inside America's Billion-Dollar Weed Business: The Grass Is Greener

Since there seems to be more interest in medical marijuana now, he said maybe more researchers will embark on these kinds of studies.

"I hope so," he said.

For patients like O'Neil, the research couldn't come soon enough.

O'Neil was diagnosed with PTSD and a lower lumbar spinal injury after he was deployed twice: During the 2003 "shock and awe" bombing in Iraq and again after the 2004 tsunami in Indonesia. After that, he took more than 30 pills a day, including OxyContin and Xanax, not to mention drugs to treat side effects like stomach issues and erectile dysfunction. "The candy shop" is what he and his buddies used to call part of the VA hospital.

O'Neil was eventually also diagnosed with a substance abuse problem and put on Suboxone to wean himself off opioids. But O'Neil realized he was just as addicted to the Suboxone, and he was still taking dozens of pills each day. That was when he decided to start using marijuana instead, even though it was against the rules. But it worked.

"When I would start to get sick, start to get those feelings, the crawling of the skin — I would just smoke pot," O'Neil said, referring to withdrawal symptoms. "It was that simple."

Instead of numbing himself to the PTSD and other physical pain, he used marijuana to make it easier to work through those mental and physical issues and learn his limits, he said.

"Cannabis is much more than just a medicine," said O'Neil, who started his own chapter of Weed for Warriors. "It's a medium for individuals to step back into some sort of social environment... As far as veterans with PTSD, it's being able to cope and get through the emotions but still feel them. You can't do that on the pills. You get flat."

And he wants the research to continue, he said. "I think we've only scratched the surface."