Botox injections are used for many medical purposes including migraine, anal fissures. The amount of botox getting into milk is low based on the research on one mother who caught botulism from eating fermented salmon eggs. She continued to breastfeed. No botulinum toxin or botulism was found in the breastmilk or the baby. The doses that are used medically are far lower than that which would have caused the mother’s botulism so the amount in breastmilk is assumed to be too low to produce adverse effects.
Hale also comments that when Botox is injected into the muscle, it produces a partial chemical denervation resulting in paralysis of the muscle. When injected properly, and directly into the muscle, the toxin does not enter the systemic circulation. Thus levels in maternal plasma, and milk are very unlikely. Waiting a few hours for dissipation of any toxin would all but eliminate any risk to the infant. Also, avoid use of generic or unknown sources of botulinum toxin, as some are known to produce significant plasma levels in humans. (Hale TW Medications and Mothers Milk online version accessed May 2020)