The Food and Drug Administration (FDA) on Friday issued a warning against the use of anti-wrinkle drug Botox and a competitor, saying that children given the drugs for muscle pain have died.

FDA officials said that Botox Cosmetic and competitor Myobloc have been linked to dangerous botulism symptoms, where muscles used for breathing and swallowing could be paralyzed or weakened.

Botox Cosmetics and Myobloc use botulinum toxin, which blocks nerve impulses in relaxing the muscle. Botox is best known for relaxing the facial muscles resulting in smoothing out wrinkles.

The FDA warned that the side effect could be potentially fatal if the injection spreads to other parts of the body. It also said it was still investigating.