But they won't immediately change how doctors treat MS, says University of Utah neurologist Stacy Clardy. "This is not being proposed as a treatment for MS. The academy is saying this may be an option for one symptom."
And while having a new option for reducing symptoms is exciting and welcome, there are drugs available to treat spasticity, "with which we have a fair amount of familiarity," said Clardy.
"At the present time I don't think it's going to make a difference in anyone's practice, because these [cannabis therapies] aren't [U.S. Food and Drug Administration] approved."
The academy looked at whole plant cannabis extract pills and oral sprays approved for use in Canada and parts of Europe and two synthetic, or man-made, forms of tetrahydrocannabinol (THC), the chemical in marijuana that gives users a high.
The synthetic drugs, dronabinol (Marinol) and nabilone (Cesamet), are approved by the FDA to ease nausea and vomiting in cancer patients and loss of appetite in patients with AIDS, but not for treating MS.
The guidelines say there's "strong" or "moderate" evidence that these therapies alleviate muscle spasticity and pain, but that they're "probably ineffective" for treating urinary incontinence and tremors.
The authors cite two small studies showing pot smoking has muscle relaxing effects, but concluded the "data are inadequate to support or refute use of smoked cannabis."
They stress that the safety of oral therapies is not known and there's isn't enough information to know how they might interact with other prescription drugs.
Side effects, including seizures, dizziness, thinking and memory problems and depression, can be serious, especially since MS patients are at increased risk for depression and suicide, the authors said.
"People with MS should let their doctors know what types of these therapies they are taking, or thinking about taking," said lead author of the guidelines, Vijayshree Yadav with the Oregon Health & Science University in Portland.
Alternative therapies are used by 33 to 80 percent of MS patients, particularly by women with higher education levels and those in poorer health, Yadav said.
But cannabis aside, very few of them work, she found.
There's "weak" evidence that ginkgo biloba and magnetic therapy reduce tiredness, the guidelines say.
Evidence is also "weak" for reflexology's purported easing of tingling, numbness and other unusual skin sensations. Bee sting therapy, a low-fat diet with fish oil, and a therapy called the Cari Loder regimen show no benefits.
And bee stings can cause a life-threatening allergic reaction and dangerous infections, the academy found.
Support from the National Multiple Sclerosis Society
According to the National Multiple Sclerosis Society: "The question of whether marijuana produced from the flowering top of the hemp plant, Cannabis sativa should be used for symptom management in multiple sclerosis (MS) is a complex one. It is generally agreed that better therapies are needed for distressing symptoms of MS including pain, tremor and spasticity. Still, there are uncertainties about the benefits of marijuana relative to its side effects. The fact that marijuana is an illegal drug in many states and by federal statute ... further complicates the issue.
The Society supports the rights of people with MS to work with their health care provider to access marijuana for medical purposes in accordance with legal regulations in those states where such use has been approved. In addition, the Society believes that more research is needed to better understand the benefits and potential risks of marijuana and its derivatives as a treatment for MS."