ST. PAUL — One of Minnesota’s medical marijuana manufacturers has raised its prices substantially after less than a month in business, adding to a cost that many patients are already struggling to cover.

Dr. Kyle Kingsley of Minnesota Medical Solutions told the Associated Press Thursday that the company raised prices on its pills, vapors and liquids by 15 percent to 20 percent last week. The company also reduced the size of a discount for low-income Minnesota residents, he said.

“That’s not something we do lightly. The reality is, it’s very expensive to do this,” he said.

Kingsley said the price changes were driven largely by an unexpected influx of patients who qualified for the low-income discount. And low enrollment since medical marijuana sales began July 1 has kept savings from producing in mass quantities out of reach. Just 220 patients were registered to buy medical marijuana with the state as of July 23.

The price increases, which weren’t announced in advance or publicized, riled some patients faced with big bills for the medication. Insurance doesn’t cover medical marijuana.