For medical marijuana patients, the drug is not only for getting high. It offers relief from pain, nausea and other symptoms of illness.

Now, medical marijuana patients are worried that supply of their medicine is in "grave danger" when legal recreational marijuana goes on sale.

"No regulations have been drafted that would protect the patient supply in times that the demand outweighs the supply," said Michael Latulippe, development director for the Massachusetts Patient Advocacy Alliance, which represents medical marijuana patients.

According to experts who have been following the marijuana industry in other states, Massachusetts is likely to face a shortage of marijuana once legal sales begin in July. That is because it will take time for the industry to ramp up and develop enough growing facilities to meet the demand.

"I look at what happened in Nevada last summer, Colorado, Washington, Oregon when they opened retail," said Peter Bernard, president of the Massachusetts Grower Advocacy Council. "All of them ran out in a week or less."

Bernard added, "We're talking about opening this summer in the middle of tourist season."

Today Massachusetts has 22 registered dispensaries selling medical marijuana and 46,300 registered medical marijuana patients. Nine other dispensaries are in the final stages of the registration process before getting permission to sell. There is no way to know how many stores will apply for licenses to sell recreational marijuana, since the licensing process does not open until April.

"If they do not create rules and regulations governing the virtual separation of medical or adult use cannabis in a smart way, we could end up with a situation where patients run out of medicine in July," said Latulippe, who is on the state's Cannabis Advisory Board.

Nichole Snow, president of the Massachusetts Patient Advocacy Alliance, said medical marijuana patients consume 29,000 ounces of marijuana a month. There is no data available on how much marijuana existing cultivation facilities are able to produce.

The alliance has been asking for the creation of a reserve supply so patients can continue to have access even if dispensaries sell out of recreational products.

So far, nothing has been included in the Cannabis Control Commission's draft regulations to protect the medical marijuana supply, although the commission is still working on writing the final rules.

One potential solution would be for the Cannabis Control Commission to require dispensaries to set aside a specific amount of their stock for medical patients. Another would be to limit the amount someone can purchase, which some dispensaries may do on their own if they face shortages. Bernard said getting cultivation licenses out quickly will also help increase supply.

For now, it is up to individual dispensaries to decide what to do. Several dispensary officials said they are committed to protecting the medical marijuana supply.

Revolutionary Clinics in Somerville plans to look back 60 days beginning March 15, then set aside 60 days worth of supply for medical patients after July 1.

"We do feel there will be shortages, and the last person who should have to suffer is patients," said Erik Williams, a spokesman for Revolutionary Clinics. "We are taking concrete steps right now to ensure our patients have the medicine they need."

Increased demand could also drive up the cost of marijuana.

Williams said Revolutionary Clinics cannot commit to pricing but does not expect a large price increase in medical marijuana.

Theory Wellness plans to keep its Bridgewater dispensary open only for patients, while selling recreational and medical marijuana in Great Barrington. Brandon Pollock, CEO of Theory Wellness, said, "We got into this for the patients, so that's our first priority, is making sure we can continue to serve them and not raise prices on existing products."

Pollock said the dispensary is tracking sales weekly, and officials plan to set aside enough inventory for patients. He noted that some medical products are not allowed to be sold on the recreational market because the doses are too high.

Norton Arbelaez, director of government affairs for New England Treatment Access -- which grows marijuana in Franklin and sells in Brookline and Northampton -- said some of the potential supply problem will be mitigated by the fact that some people will continue to buy on the black market during the transition.

"It will take some time for the regulated and taxed and tested marketplace to supplant and replace the gray and black market," Arbelaez said.

Arbelaez said NETA, like other companies, is also investing in new infrastructure and plans to double the amount of product available in advance of legal recreational sales.

"If for some reason down the line we have to choose whether to limit access to medical or recreational, we will limit access to recreational before we do medical," Arbelaez said. "We don't expect that to happen."

Arbelaez noted that medical marijuana also has the advantage of not being taxed in the way recreational marijuana is. He said he does not anticipate price spikes.

Will Luzier, political director at the Yes on 4 Coalition that pushed for legalization, said a potential marijuana shortage is a concern, and he supports efforts to ensure the medical marijuana supply is protected. "It's important for medical patients to have their medicine," Luzier said.