Japanese drugmaker Kobayashi Pharmaceutical has announced that it is voluntarily recalling a line of dietary supplements containing beni kōji fermented rice after reports of kidney problems from 13 people, including six who required hospitalization.

The Osaka-based drugmaker announced Friday that, of the six hospitalized, two suffered symptoms serious enough to require temporary dialysis. Five of the six have been discharged from the hospitals, the firm said.

The firm is recalling about 300,000 packs of five supplements containing fermented rice and calling on customers who bought them to stop taking them immediately.

The 13 who were reported to be affected have experienced kidney problems, with symptoms such as swelling in their limbs, a sense of fatigue and changes in the color of their urine.

The products were advertised as having health benefits by lowering bad cholesterol, blood pressure and visceral fat.

Beni kōji is rice fermented with monascus purpureus, a species of reddish-purple mold, and is traditionally used for food coloring.

While the specific cause of the beni kōji-related health problems has yet to be identified, the firm said it is looking into the possibility that the product contains a previously unknown toxic substance, noting that it is investigating the cause with the help of university researchers and hopes to come up with results within one or two months.

The firm had received reports of health problems between mid-January and March 15, with the users being both men and women in their 40s up to their 70s.

The problem may extend far beyond Kobayashi Pharmaceutical. Kyodo News reported Sunday that the drugmaker had supplied beni kōji to about 50 food and beverage manufacturers since 2016 for use in sake and confectionary products.

Takara Shuzo Co. said Sunday it will recall a sparkling sake product containing red kōji supplied by Kobayashi Pharmaceutical. The strawberry-flavored Mio Premium sake had been on sale as a limited edition product since January.