The maker of Robitussin cough syrup is recalling several lots of products containing honey due to contamination that could pose a serious risk to people with weakened immune systems.

Haleon’s recall covers eight lots of Robitussin Honey CF Max Day Adult and Robitussin Honey CF Max Nighttime Adult, which were distributed to stores and pharmacy suppliers. The Food and Drug Administration posted the company’s announcement to its website Wednesday.

The products may contain dangerously high levels of yeast, the company said in an emailed message Thursday. Yeast is a natural component of honey, but the levels detected by the company were “beyond allowed measurements,” Haleon said.

Ingestion of the contaminated syrup could result in severe fungal infections that would be potentially dangerous for people with weakened immune systems, such as organ transplant recipients or those with HIV. Several million people in the U.S. have conditions that impair the immune system’s ability to fight off infections.