Botulinum toxin, best-known as a cause of lethal food poisoning, has been found to be safe and effective in small doses in treating a variety of muscle spasms, a National Institutes of Health committee announced last week.

The toxin, obtained from a bacterium that causes botulism food poisoning, has been used successfully to treat involuntary clenching of muscles in the eyelids, throat, face and the vocal cords, the panel said.

It also shows promise in the treatment of stuttering, misalignment of the eyes and for cramps experienced by musicians, writers and typists.

Roger Duvoisin, a New Jersey physician who chaired the NIH panel, said the toxin is an example of a highly lethal poison that can be beneficial in small doses.

He said that hundreds of thousands of Americans suffer from some form of muscle spasm that can be treated by the toxin.

Very small doses injected directly into specific muscles, Duvoisin said, have the ability to block signals from nerves to muscles. This action will halt involuntary muscle spasms that can distort facial expressions, cause eyelids to close tightly so that victims have to pry them open by hand, or the voice to jam when the vocal cords are involved. Unbalanced muscles can also cause eyes to be crossed or pointed fixedly to the side.

Duvoisin said the toxin injections work for only a few months and then the effect wears off. He said there is no apparent limit on the number of injections that can be used without side effects.

The therapy takes a high degree of expertise and only a limited number of doctors are skilled in its use, he said. A round of injections with the toxin can cost from $400 to $1,800, according to Duvoisin.