In marijuana debate, both sides can point to the science

If marijuana were a new discovery, without cultural and political baggage, "it would be hailed as a wonder drug," wrote Dr. Lester Grinspoon last year. The Harvard psychiatrist has advocated for medical marijuana for decades.

Yet a gap has persisted between what many believe about medical marijuana's potential and what scientists could prove. Now recent research has applied the same rigor that would be used on any new pill to testing marijuana.

The results, so far, give ammunition to both sides of a debate at the Minnesota Legislature, where a medical marijuana bill has passed the Senate and a House committee. It would make Minnesota the 13th state to allow medical uses within strict limits.

Politics aside, what does science conclude at this point about medical marijuana?

No argument

Scientists agree on one thing: the active ingredient in marijuana, THC, has some healing powers. In 1985, the U.S. Food and Drug Administration (FDA) approved the pill Marinol, a synthetic form of THC, to relieve nausea and vomiting from chemotherapy. A few years later, the pill also won FDA approval to stimulate the appetite of people wasting away from AIDS or cancer.

Pill vs. plant

Government scientists agree research shows smoking marijuana gets THC into the bloodstream faster than a pill.

But the FDA argues that marijuana must go through the same hurdles as any medicine to be proven safe and effective, and that it's impossible to ensure the dose and potency of something that grows wild. The FDA has never approved any medicine to be smoked.

Also, marijuana is listed as a Schedule I controlled substance, the most restricted class of drugs in federal law. It's a category reserved for drugs with a high potential for abuse, no accepted medical uses and no safety data for medical use.

Promising research

Supporters claim marijuana can help treat hundreds of conditions, from depression to malaria.

In 1999, the Institute of Medicine (part of the National Academy of Sciences) conducted the most extensive review of scientific literature of marijuana and concluded that its chemical compounds "likely have a natural role in pain modulation, control of movement and memory."

Until recently, "medical studies, at least meeting modern standards ... have been lacking," said Dr. Igor Grant, director of the Center for Medicinal Cannabis Research at the University of California, San Diego, which has spearheaded much of the latest research. "There has been quite a lot of anecdotal evidence, uncontrolled research, that there may be benefits."

To win over scientists, the research generally has to show that a drug works better than a placebo, and that neither scientists nor subjects knew who was getting the real thing.

Since 2007, a handful of government-approved studies at the University of California have found that smoking marijuana can help relieve neuropathic (nerve) pain from injuries or diseases such as AIDS and cancer. In each case, half the volunteers were given marijuana and the other half a fake substitute. They found a measurable difference.

But researchers also turned up some cautionary notes. One study, released in October, tested three different concentrations of marijuana, and found only one -- the middle dose -- provided "moderate pain relief." The lowest dose showed no effect and the highest dose actually increased pain, the study found. Another study found pain relief came with a worrisome downside: psychological impairment.

Mixed results

Scientists have also tested marijuana's active ingredients on other conditions, such as glaucoma and multiple sclerosis. Results have been mixed and scientists say there's no proof that it's better than existing drugs.

Studies suggest THC can reduce eye pressure associated with glaucoma, but that the effects are shortlived; and scientists worry that the side effects, especially on the heart, could pose an even greater danger to elderly patients.

With multiple sclerosis, studies have found fleeting improvement in spasticity, or muscle contractions, but that THC worsened patients' balance and control. The MS Society has called for more study.

The downside

Like tobacco, it contains toxic chemicals that can endanger pregnant women and cause cancer, lung damage and pneumonia.

The future

Scientists are testing vaporizers and skin patches as alternatives to smoking marijuana.