The stock of medical marijuana products at licensed Michigan businesses will soon change, as a result of new guidance from state officials.

Effective immediately, licensed medical marijuana provisioning centers can no longer stock their shelves with products grown by caregivers, the Marijuana Regulatory Agency announced Thursday in a press release.

Licensed shops can only buy from state-licensed growers and processors. Caregivers, however, will be allowed to sell to state-licensed growers and processors -- who will be required to test the product and enter it into the state’s tracking system.

The switch away from the illegal supply of caregiver weed to the regulated market was supposed to occur April 1, but was delayed for a month due to a barrage of lawsuits filed against the state in a separate but entangled issue over the ability of unlicensed pot shops to operate.

Court of Claims Judge Stephen Borrello issued his orders two days ago -- which allow unlicensed pot shops to stay open until 60 days after officials decide on their license applications. Borrello left the issue of caregiver product up to the Marijuana Regulatory Agency to decide.

Now the embattled medical marijuana market will switch over to regulated product as its main source.

Corporate mega-growers have criticized the use of caregiver marijuana for the past five months, as it has tested positive for E. coli, Salmonella, mold, lead and other heavy metals. No illnesses have been reported to the state from its use.

Licensed growers have also complained that competition from caregivers is hurting their business.

In turn, patients and caregivers have lashed out against the corporate growers. They claim mega growers aren’t manufacturing the medicinal products that they need and are only focused on products that recreational users will want.

Jerry Millen, owner of a Walled Lake licensed provisioning center, predicted the market will not respond well as a result of the state’s latest regulatory action.

“I’m afraid this is going to make the black market explode 100-fold,” Milen said.

Caregivers won’t be keen to start new business relationships with the same licensed growers that insulted their products last week, Millen said. Instead, caregivers will likely flood the unlicensed pot shops that the state has allowed to open with their product -- a black market with lower prices and more medicinal products that patients will likely seek out, Millen said.

Michelle Donovan, a lawyer with Butzel Long who sued the state over the caregiver supply issue, also predicted a surge in the black market as a result of the state’s action.

“It’s going to allow the caregivers to sell their products directly to the dispensary centers that don’t have their state license,” Donovan said. “Do I want to drop mine off and pay to get it tested, or do I go down the street?”

-- Amy Biolchini is the marijuana beat reporter for MLive. Contact her with questions, tips or comments at abiolch1@mlive.com. Read more from MLive about medical marijuana.