Marijuana dispensaries may have to quality test in Mass.

Proposed state rules for the medical use of marijuana, which regulators will debate Wednesday, would make Massa­chusetts one of the few states that require marijuana dispensaries to test their products for contaminants such as heavy metals and pesticides, but specialists say it is easier to mandate testing than to do it reliably.

Few credible labs will test marijuana products for potency or contaminants for fear of losing federal government contracts, because medical marijuana is not sanctioned by federal law, say researchers who study the medical marijuana industry. That means testing will probably be left up to the dispensaries, they said.

“If you are going to talk about marijuana as medicine, you need to think about how you produce it and ensure its safety for patients,” said ­Rosalie Liccardo Pacula, a ­senior economist and codirector of the Drug Policy Research Center at RAND Corporation, a California-based nonpartisan research institution.

Pacula, who received a ­National Institutes of Health grant two years ago to study state marijuana laws, said her research has found few states that mandate testing.

Americans for Safe Access, a nonprofit that advocates for ­research and medical use of marijuana, will be submitting written comments suggesting a system of state-licensed, independent labs that would test marijuana but that would not be at risk of federal sanctions because they would not test narcotics and other federally regulated drugs.

“We would absolutely like to see third-party testing,” said Jill Lamoureux, the organization’s program director. “It’s more ­reliable.”

Massachusetts became the 18th state to adopt a medical marijuana law after voters ­approved a ballot referendum last November, and that measure required the Department of Public Health to issue regulations to implement the law.

Last month, the department issued 45 pages of draft regulations, which say dispensaries are responsible for testing marijuana products for contaminants including mold, mildew, metals, and pesticides, but do not specify how often.

They also include a section on inspections of dispensaries, known as Medical Marijuana Treatment Centers. The rules state that inspections may be conducted “at any time without prior notice” and stipulate that all areas of the centers and all records are “subject to such inspec­tion.” But inspections would not be mandatory under the proposed rules.

The section is similar in wording to Massachusetts rules regarding oversight of pharmacies, an issue that has sparked heightened state scrutiny after a deadly fungal meningitis outbreak last year was tracked to drugs produced at a Massachusetts specialty pharmacy.

While regulators have long had the authority to inspect pharmacies “at any time without prior notice,” under state rules, they seldom did, instead opting to review pharmacies only when they opened, ­expanded, or drew complaints. It was only after contamination at New England Compounding Center in Framingham was linked to dozens of meningitis deaths and hundreds of illnesses last fall that Governor Deval Patrick ordered annual surprise inspections of similar pharmacies. That ruling has not since been codified in state law or regulations for pharmacies.

Asked about inspections of dispensaries, Dr. Lauren Smith, interim state health commissioner, declined through a spokesman to be interviewed.

After the Globe asked about the lack of mandatory inspections, spokesman David Kibbe said Tuesday: “The regulations are not final, so I cannot predict what the final regulations will look like, but I can tell you that DPH will conduct unannounced inspections of these facilities, just as the department does with pharmacies.”

Rules on inspections in other states vary widely, and mandatory testing of products has received little attention elsewhere, said Pacula.

California, which was the first state to adopt marijuana legislation in 1996, does not ­require testing and has very little state oversight. It leaves the issue of inspections up to each city that licenses a facility, a system that has produced widespread confusion, Pacula said.

“California is an example of how not to do it,” she said.

On the other end of the spectrum is Maine, which is in the midst of tightening oversight after employees at the state’s largest dispensary company told regulators about pesticide use by growers, which is prohibited under Maine rules. The Massa­chusetts draft rules also prohibit pesticide use.

Officials at the Wellness Connection had assured Maine inspectors they were not using pesticides during its most ­recent annual inspection, but after state officials received calls from concerned employees, the state sent inspectors back to the company’s Auburn cultivation site last month, said Joan Smyrski, an assistant ­director at Maine’s Division of Licensing and Regulatory Services. “When we went back, we opened every closet and every locked room, and field officers found the pesticides,” she said.

She said Maine prohibits pesticide use because research is lacking about health effects.

“This is not like putting pesticides on your home-grown ­tomatoes, because you can’t wash marijuana,” Smyrski said. “We still can’t say that when you ignite it, heat it, and inhale it that it’s not causing duress to someone in end-stage illness.”

State records show inspectors found nine pesticides and more than 20 other violations, including bags of marijuana in varying stages of processing that included labels indicating “mold,” or “bugs.”

“When employees were asked about the intentions for the contents of these . . . they ­reported that they would be required to package [for sale] what they could and that the ­remainder would be disposed,” the records state.

Wellness Connection, which owns dispensaries in four communities and two cultivation sites, recently agreed to correct the problems, Smyrski said. Regulators have stepped up unannounced inspections of the state’s eight dispensaries.

“We are in the very early stages of looking toward the process of needed lab equipment and how to perform sample testing in a legal and sound manner,” Smyrski said. “This is an extremely complex issue due to our federal partners not recognizing marijuana as a legally allowed medicine, and then the various barriers we have encountered around nonallowance of testing in labs that ­receive federal funds.”