US FDA has approved Botulinum Toxin Type A (Botox) to treat severe underarm sweating known as "primary axillary hyperhidrosis" that cannot be managed by topical agents such as prescription antiperspirants. Botox has already been approved for several other purposes. This approval allows the product's manufacturer, Allergan Inc, Irvine, to market Botulinum Toxin Type A for this new indication, an FDA release said.

Botulinum Toxin Type A is a protein produced by the bacterium Clostridium botulinum. When used to treat primary axillary hyperhidrosis, small doses of an injectable form of the sterile purified botulinum toxin stop release of the chemical messenger acetylcholine, temporarily blocking the nerves in the underarm that stimulate sweating.

Botox was first approved in December 1989 to treat two eye muscle disorders (blepharospasm and strabismus). Since then it has been approved to treat cervical dystonia, a neurological movement disorder causing severe neck and shoulder muscle contractions. Most recently, in 2002, it was approved as Botox Cosmetic to temporarily improve the appearance of moderate to severe frown lines between the eyebrows.

In two placebo-controlled, multi-centre, randomized, double-blind clinical trials involving over 600 adults, those who received Botox had significantly reduced underarm sweating as compared to the placebo group. In one study, four weeks after being injected, the percentage of people showing a 50 per cent reduction in sweating was 91 per cent in the group receiving Botox compared to 36 per cent in the placebo group. In another study, the average duration of response following the first treatment was 170 days.