As Health Canada reviews the use of Botox, a Calgary study has found the toxin can seep beyond its target area and is harder to control than many first thought.

The botulinum toxin, which is used to smooth out wrinkles in cosmetic procedures, is also used to relax spastic muscles caused by cerebral palsy or a stroke.

Walter Herzog, a researcher at the University of Calgary, used Botox in his study of how muscle weakness contributes to joint degeneration. His team found that the toxin passed easily from the targeted muscle into surrounding ones, weakening all the muscles in the area.

"Many people believe that when Botox is injected into a single muscle, it stays there," Herzog said Tuesday. "This research shows that it is not that easy to control."

The kinesiology professor said the next step is to determine how long it takes for Botox to pass into other areas and what dose could safely target a specific muscle while minimizing seepage.

Health Canada announced a review of use of the toxin last week, after the U.S. Food and Drug Agency warned that Botox was linked to severe side effects and the deaths of children with cerebral palsy who were being given large doses to treat limb spasms.

Herzog's study is available online and will be published in the upcoming hard-copy edition of the Journal of Biomechanics.