Certain chemicals in marijuana may kill cancer cells, shrink tumours and prevent the formation of blood vessels that feed tumours.

That's what the United States' National Cancer Institute said when reporting its findings from preclinical trials - the kind of research that typically leads to more in-depth testing. But nearly half a century ago, the folks who write the cheques for the cancer institute - the US government - proclaimed marijuana to be a stoner-only drug and stamped it Schedule I, lumping it in with heroin and LSD. That early war-on-drugs salvo cut the world's biggest funder out of medical marijuana research.

Had the US written cheques back then to turn the big research labs loose, we might know by now that marijuana is nothing more than a good buzz, as promising as the smoke that spills out of Jeff Spicoli's van in the 1982 film Fast Times at Ridgemont High. Or, who knows? Marijuana-based drugs could be improving lives today. Maybe even saving some.

Because while America was just saying no, research - much of it from other countries - has shown that marijuana derivatives called cannabinoids, such as cannabidiol (CBD), can trigger the body's natural defences to fight things such as cancer, Alzheimer's, multiple sclerosis, diabetes, Crohn's disease and epilepsy.

A Canadian study concluded cannabis reduced pain and improved sleep for sufferers of neuropathic pain. Research is being conducted in Israel on marijuana as a treatment for traumatic brain injury.

Health organisations, such as the American Cancer Society, increasingly say the Schedule I label stands in the way of scientific research. But the federal government continues to stick to its Richard Nixon-era stance - even when calls for change come from its own agencies.

"That's my definition of chaos," says J. Michael Bostwick, a psychiatrist at the Mayo Clinic, in Minnesota, and author of Blurred Boundaries: The Therapeutics and Politics of Medical Marijuana.

"The federal government needs to change its position so this research can take place," Bostwick says.

It's a catch-22: marijuana being on the Schedule I list impedes research that could show it doesn't belong there.

Who can change this? That's another fight.

The easiest route would be for the Drug Enforcement Administration to act. But, in 2011, the agency rejected a petition, filed nearly a decade earlier, to do so after hearing opposition from the Department of Health and Human Services.

It appears now that change could come from Congress. In March, Rand Paul, a Republican presidential candidate with a libertarian bent, helped introduce legislation that would reclassify marijuana as a Schedule II drug. That would mean the federal government recognises its medical value but that the drug can be abused, much like prescription opiates. The 23 states that have approved medical marijuana would also be protected from federal intervention. The administration of Barack Obama has made it clear that it will let those states play by their own rules but his successor is not obligated to do likewise.

There's still plenty of opposition. Opponents typically argue that conventional drugs are safer and that "medical marijuana" is simply an incremental ploy to facilitate the sale of recreational pot. Indeed, in California and elsewhere it's become common for doctors to set up shop in or next to dispensaries specifically to diagnose dubious conditions such as pain from old high school football injuries.

"You're not seeing a lot of medical support for marijuana and these state legislatures are giving pot a free rein," says Eric Voth, a physician and long-time marijuana opponent, who heads the Institute on Global Drug Policy and speaks on behalf of the national Drug Free America Foundation.

A common volley from advocates is that doctors who oppose marijuana research are probably trying to protect the prescription-drug business. But if the government should loosen its grip, Mahmoud ElSohly would instantly become the country's best-known pot farmer.

He's got 12 acres up and growing in the middle of the University of Mississippi campus, where the spring was warm and rainy. A scientist and professor, ElSohly heads the federal government's marijuana patch. His crop is where any research project approved by the US Food and Drug Administration (FDA) would get its plants.

A Kansas man with ALS (amyotrophic lateral sclerosis), or Lou Gehrig's disease, says legalisation of marijuana for medical purposes is long overdue. He's 55, a father of five and grandfather of six, and uses marijuana to help with pain and spasticity. He keeps a second home in Colorado, where marijuana is legal.

"I used to take 30 to 50 pills a day - OxyContin, oxycodone, hydrocodone," says the man, who asked that his name not be used. "Now I'm down to zero and not zoned-out on opiates all the time."

So these cannabinoids - what do they do?

Scientists say humans have a unique communication system in the brain. When receptors are triggered by cannabinoids, they transmit signals throughout the body. This "endocannabinoid system" provides the infrastructure for marijuana's effect on humans.

Sometimes that's simply the euphoric feeling of getting high. But researchers increasingly find that those chemical charges may go through the body and kill cancer cells, ease neuropathic pain, calm seizures from epilepsy, help control blood sugar, relieve glaucoma's intraocular pressure and provide a host of other benefits.

All this has changed minds - perhaps most famously that of Sanjay Gupta, CNN's chief medical correspondent and a neurosurgeon. For years an opponent of medical marijuana, Gupta apologised in August 2013.

"We have been terribly and systematically misled for nearly 70 years in the United States, and I apologise for my own role in that," he said.

The new information has also led to a changed political climate in which polls show most Americans now favour the legalisation of marijuana. The findings prompt even long-time marijuana opponents to acknowledge their promise. Voth says that something called "Charlotte's Web", a CBD with little of the buzz component of marijuana, appears to be effective in treating children with epilepsy. But he and others reject many other claims about marijuana.

In December, Samuel Wilkinson, at Yale University's School of Medicine, released a study that showed treatment of post traumatic stress disorder suffered when patients smoke marijuana. Wilkinson previously released a paper that linked marijuana use to schizophrenia. And while the American Glaucoma Society says that marijuana eases intraocular pressure, the relief lasts only three hours, so patients need to smoke several times a day. The society advises against marijuana use as a treatment.

It's hard to imagine the FDA would ever approve "crude marijuana" - joints and bong hits that channel smoke to the lungs - but derivatives can come in many smokeless forms, where the components and dosages can be better controlled.

That said, many patients would still champion the healing power of a good doobie.

 

A summary of other research:

Multiple sclerosis

The Multiple Sclerosis Society says studies suggest that a marijuana extract, usually administered in a spray beneath the tongue, may lessen symptoms of spasticity, pain related to spasticity and frequent urination. But a clinical trial in Britain provided unclear results. An instrument used to measure spasticity showed little improvement even as participants reported, anecdotally, improved spasticity and less pain.

"In other words," the study said, "participants reported feeling improvements that could not be confirmed by the study physicians."

John Zajicek, a professor at Plymouth University Peninsula Schools of Medicine and Dentistry, led a study to evaluate oral cannabis extract in treating 400 patients. Results showed stiffness lessened by twofold in the group taking the marijuana compared with those on the placebo. Improvements were also noted in body pain, spasms and sleep quality.

The American Academy of Neurology recognises the potential, but does not support legalisation of marijuana treatment.

Epilepsy

There's been a migration of parents to treating their children with marijuana. The poster child for this movement is Charlotte Figi, a toddler who suffered Dravet syndrome, a genetic disorder that can cause epilepsy.

"If I were Charlotte Figi's parents and lived in Colorado, I would have done exactly what they did," Orrin Devinsky, a professor of neurology and neurosurgery, and director of the Comprehensive Epilepsy Center at New York University, says on the Epilepsy Foundation's website.

In 2013, researchers in the neurology department at Stanford University released a survey of 19 parents who opted for cannabis to treat a child's seizures. These parents, on average, had previously tried 12 approved anti-epileptic drugs with little or no satisfaction.

Sixteen, or 84 per cent, reported reduction in their children's seizure frequency while taking CBD. Two said their child became seizure-free with eight reporting a greater than 80 per cent improvement.

"Parents," researchers wrote, "report a high rate of success in reducing seizure frequency with this treatment. We cannot verify the doses or the children's response to cannabis. Nonetheless, the overall positive results on seizure control suggest that further studies are warranted."

Cancer

The National Cancer Institute says preclinical trials on mice suggest cannabinoids may inhibit tumour growth and block the development of blood vessels that feed tumours. Studies also show that cannabinoids may protect against inflammation of the colon and may reduce the risk of colon cancer. Another study, on mice, showed that a compound called delta-9-THC killed the cells in liver cancer and may have the same effect on lung cancer and breast cancer cells.

A study of cannabidiol in oestrogen cells showed that it caused cancer cell death while leaving normal cells alone.

Despite advances in pharmacology, vomiting and nausea associated with chemotherapy remain a distressing part of cancer treatment. Trials show that patients experience less of those effects with marijuana derivatives and smokable marijuana.

Still, the cancer institute and the American Cancer Society say more proof is needed before they can recommend marijuana.

Crohn's disease

A prospective trial at Meir Medical Centre, in Israel, showed complete remission in five of 11 patients suffering Crohn's disease who were given cannabis twice daily. Authors of the study said it had been reported for years that marijuana lessened the painful symptoms of the inflammatory bowel disease, but the findings had not been proven in a controlled trial.

The study compared 21 patients who did not respond to conventional treatment. Half were given marijuana cigarettes. The other half were given a placebo - marijuana cigarettes with the THC removed.

The results, published in Clinical Gastroenterology and Hepatology, showed improvement in the group treated with the THC-intact cannabis. Those subjects also reported improved sleep and appetite.

Alzheimer's disease

In findings published in the Journal of Alzheimer's Disease, researchers at the University of South Florida (USF) say delta-9 THC may prevent the abnormal production of amyloid beta, the culprit found in most ageing brains that may cause the disease.

"Also, the low concentrations of THC enhance mitochondrial function, which is needed to supply energy to a healthy brain," said Chuanhai Cao, a neuroscientist at the Byrd Alzheimer's Institute and the USF's college of pharmacy.

"This shows great potential."

TO ALL OF THIS, William Brook O'Shaughnessy might have said, "Well, yeah."

O'Shaughnessy, born in 1809, was an Irish physician known for his early work in India using cannabis to treat rheumatism, infant convulsions and chronic pain. He is widely considered to be the man who introduced marijuana into modern medicine.

Without him, two cannabinoids - dronabinol and nabilone - approved by the FDA may not be in use today.

Advocates are pushing for more and they are not buying the argument that marijuana can be dangerous and abused. Look at the prescription opiates, such as OxyContin, that are not only addictive but have been blamed for many deaths, they say.

Ethan Nadelmann, executive director of the Drug Policy Alliance, says the argument against marijuana as a medicine is a combination of politics and business: "It's not a medicine if it's not made by pharmaceutical companies or approved by the FDA."

As for his organisation's work, he says, "We're not doing this because we're pro-marijuana; we are pro-responsible drug policy."

At this point, even Voth thinks change is coming.

"There is tremendous pressure out there for medical marijuana," says the physician . "So no, I won't be surprised when it happens."

The Kansas City Star