Medical marijuana researchers have discovered several compounds in the drug that could have therapeutic value. | Dank Depot/ CC By 2.0
SAN JOSE, California — Humans have been using cannabis to relieve pain for about 5,000 years but robust, federally-approved research on marijuana's therapeutic value is just starting to emerge. At the 2015 AAAS Annual Meeting, researchers who have been studying the plants' diverse chemical compounds reported some promising initial results.
The discovery of more than 100 cannabis compounds called cannabinoids over the past several years — along with the identification of an innate cannabinoid system in the human brain and the generation of many synthetic cannabinoids in the laboratory — has led to unprecedented insights, they said.
Animal models and a limited number of human trials have shown that, in addition to THC — the cannabinoid known primarily for its psychoactive effects — compounds such as THCV, cannabigerol, and cannabidiol have medicinal effects on a wide range of afflictions, including chronic pain, nicotine addiction, and spasticity. However, it will take much more research to determine the right combinations of compounds to treat particular problems, as well as the appropriate dosages and drug delivery methods, according to the researchers.
"It's become clear that many of the other cannabinoids have potential therapeutic activity, but it's still too early to tell whether that's going to translate into clinical trial data or not," said Mark Ware from McGill University Health Centre in Montreal, Canada. "This web of intriguing compounds is what's making it so exciting and so interesting, but also so challenging."
"It's clear that the weight of evidence now is such that cannabinoids are analgesic drugs," Ware added. "They're not powerful analgesic drugs; their effects are modest. But they're additional tools in the analgesic toolbox that we use when we're treating patients."
Audio interview: Clinical studies have shown that cannabis does help patients experiencing various type of pain, though larger trials with more diverse populations are needed, said UCSD researcher Igor Grant. | AAAS/Carla Schaffer
Roger Pertwee from the University of Aberdeen in the United Kingdom, who has studied cannabinoids since 1968, highlighted the brain's own cannabinoid system, which modulates pain, mood, memory, appetite, and more, as an important test site for research.
"There are chemicals in our bodies that act like cannabis, and they target the same sites as THC," he said. "It begs the question of why on Earth we have these receptors in our bodies."
Attempting to answer that question, he and other researchers have begun to uncover a network of cannabis receptors and cannabinoids with complex and sometimes counterintuitive interactions. Some of them relieve pain or nausea without inducing any kind of "high." Others seem capable of relieving the symptoms of profound psychiatric disorders. Although previous studies have associated cannabis use with schizophrenia, the latest data suggests that some cannabinoids actually have anti-schizophrenic effects.
The well-known short-term effects of THC, which include cognitive and motor impairments, don't seem to impart any long-term damage to adult brains, said Igor Grant from the University of California, San Diego. But he suggests that the compound likely has negative effects on young, developing brains — and that there is an increased risk of motor vehicle crashes with marijuana, particularly when it's used in combination with alcohol.
As of 2014, 23 states and the District of Columbia allow the sale of medical marijuana. | AAAS/ Adapted from research by procon.org
More clinical trials with larger numbers of participants are needed to tease out the most effective cannabis-based therapies. But the researchers believe that such studies are on the horizon, especially given the recent and rapid push for marijuana legalization in the United States and elsewhere. Still, government restrictions and the current lack of regulation will continue to hamper cannabis studies for a while at least, they said.
As for the best delivery system for patients using cannabis? Ware said that he is most excited about the vaporization of marijuana without combusting it.
"What we're trying to teach patients is that very small quantities can achieve the kind of plasma levels that give you pain relief, but stop short of the psychoactive and acute cognitive effects that we're concerned about," he explained. "If you adjust the vaporization temperature of the same plant material, it'll give off a very different profile of cannabinoids."
"This technology to adjust the temperature of the vaporizer to precisely deliver the compounds that you want…or to adjust it to get the right mix [of compounds]…is well within our reach now," he said. "Now that we have access to standard, regulated cannabis materials and now that we have labs that can do this work and accurately measure these compounds, we may be able to get somewhere."