Lansing, Mich. -- Lynn Allen was born with severe hemophilia. In 1978, Mr. Allen discovered he had been infected with HIV and hepatitis C through a contaminated blood transfusion. Now in chronic pain, the Williamston, Mich., man, once a rehabilitation counselor and social worker, is disabled, using a wheelchair to get around.

His medication of choice: medicinal marijuana, which has stimulated his appetite and allowed him to maintain his weight. He is among the growing number of Michigan residents who have received state approval to use and grow the herb for certain medical conditions under a new law passed resoundingly by Michigan voters in November.

Don’t call him a pothead, he says. He smoked weed in college but didn’t use it again for 30 years. Now he views himself as an informed consumer who has found something that works.

“There have been people within my own family that didn’t think it was appropriate until they learned more about it,” says Mr. Allen, 52. “I think that will probably be the case for a lot of people as they learn the benefits it has to offer.

“There is a lot of bias against marijuana because it isn’t a regulated prescription drug,” he adds. “In my case, we did try other medication, but this has been the most effective for me. I think it shows a lot of compassion on the part of voters and those who are trying to make the system work so that people like me can benefit from this medicine.” As Michigan works out the kinks of a new medical-marijuana law — passed by 63 percent of voters — its future success could serve as the bellwether for other states considering similar legislation.

Thus far, 13 states have passed medicinal- marijuana legislation. About a dozen more are considering bills that would allow those with serious illnesses like cancer, multiple sclerosis and AIDS to smoke marijuana to alleviate some symptoms, including nausea and loss of appetite.

“We do believe that Michigan is a precursor for other Midwestern states,” says Greg Francisco, the executive director of the Michigan Medical Marijuana Association, which is bringing together new users to help educate them and encourage ethical consumption.

“We think there are other states that are close on our heels, and it’s only a matter of time,” he said. “In the meantime, we are hearing people are relocating here — they want to live in a compassionate state. We think this has brought some migration back into Michigan.” So far, 2,377 applications for marijuanauser identification cards have been received by the state’s department of community health. Of those, 1,903 applicants have been issued registration cards, with 1,412 of those applying as patients and 496 applying as caregivers who can grow and administer the medical pot under stateGuidelines, said James McCurtis Jr., Michigan Department of Community Health spokesman.

Just 320 applications have been denied.

Applicants are typically denied because they did not properly fill out the application or they did not include the fee with the application, Mr. McCurtis said.

The state’s first medical marijuana clinic opened in the Detroit suburb of Southfield on Dec. 4. Doctors there evaluate patients and write approval forms for medicinal marijuana. The state’s clinics, however, do not sell the medicinal cannabis, but have drawn the ire of some local government leaders who fear they may open the doors for abuse and crime.

The Michigan law allows those with a doctor’s recommendation to register for permits through the state. They can possess up to 2.5 ounces of marijuana and are allowed to grow up to 12 plants in enclosed and locked facilities. They can designate a caregiver who is allowed to grow up to 12 plants per patient. Caregivers are limited to five patients.

Opponents say they fear that the excess that might be grown could make its way to the black market. A couple of Michigan municipalities — Fenton Township and Clio — are considering ordinances to ban medicinal-marijuana dispensaries.

One Detroit suburb, Royal Oak, is considering allowing sellers of medicinal marijuana to grow and sell pot in storefronts along the city’s business district, offering a transparent way to deal with the law andAllowing growers to be regulated in the open as a business. The zoning ordinance would have to be approved by city commissioners.

Mr. Francisco says clearer state guidelines are needed for not only localities trying to adapt to it fairly but also law enforcement and prosecutors along with other stakeholders as they move forward and implement the law.

“We don’t mind reasonable regulation and oversight,” he said. “We just want some clear guidelines to work with.” Some local police leaders have been vocal opponents of the Michigan medicinal- marijuana statute. Gene Basar, a police chief from Howell, Mich., who serves as president of the Michigan Association of Chiefs of Police, calls it a “terrible, terrible law” that he fears will lead to a spate of costly lawsuits.

“This is the nose under the tent to the legalization of marijuana,” Mr. Basar told the Livingston Daily newspaper.

The Michigan law has sparked concerns of lawsuits including issues over the growth of too many plants by caregivers and speculation over the possible distribution and sale of excess marijuana for recreational use. There has also been some concern that physicians who write medical-marijuana recommendations for patients could ultimately be held liable if the user was involved in an accident while under the influence.

But William J. Johnson, executive director of the National Association of Police