Public Citizen Health Research Group has petitioned the U.S. Food and Drug Administration to require the strongest possible warning, highlighted in a “black box,” on Allergan Inc’s Botox and Solstice Neurosciences Inc’s Myobloc.

The request comes following reports of 16 deaths after the botulinum toxin spread inside the body, the U.S. consumer group said on Thursday.

Botox became famous for smoothing facial wrinkles but it was also approved for medical uses such as treating cervical dystonia or rigid neck muscle. Myobloc is approved only for neck condition. An injection made with forms of the botulinum toxin block nerve impulses to muscles and makes them relax. The substance is also used off-label to stop sweating and address pain.

On sustaining their cause, Public Citizen did a safety analysis of Botox procedures from FDA records covering 1997 to 2006 and discovered 658 adverse effects from injections and 16 deaths, including children under 18. There were discovered cases of muscle weakness, difficulty swallowing or aspiration pneumonia, a serious condition caused by breathing a foreign material into the lungs.

The data comes from the drug manufacturers, so Public Citizen believes the numbers could be much higher. Therefore, the group wants the FDA to send warning letters to doctors so they seriously consider the risk of botulinum toxin.

“These significantly improved warnings to doctors and patients would increase the likelihood of earlier medical intervention when symptoms of adverse reactions to botulinum toxin first appear, and could prevent more serious complications, including death,” Public Citizen said in a petition to the FDA.

Allergan has already issued a statement saying that it is in a continuous dialogue with the FDA to ensure proper labeling.

“There are no safety issues raised in the petition that are not already addressed in the labeling for Botox,” Allergan said, according to Reuters.

The FDA will not comment about the case while the Public Citizen petition is under review, said FDA representative Karen Riley.