It's now official: Wrinkle-smoothing Botox (search) can be injected in the armpits to curb excessive sweating.

On Tuesday, the Food and Drug Administration (search) approved the long-expected new use of Botox, the latest in a range of conditions to be treated by this weakened form of the food-poisoning toxin that causes botulism.

People with a condition called "primary axillary hyperhidrosis" (search) produce four or five times the amount of underarm sweat as is normal. There are various treatments, including powerful antiperspirants, drugs to prevent sweat gland stimulation, even surgery on those glands.

Botox apparently temporarily paralyzes a nerve that stimulates sweat glands. In one study, 91 percent of patients who received Botox underarm injections saw their sweating cut in half in a month, compared with 36 percent of patients given salt-water injections.

Patients can get additional injections every few months. FDA cited one study that found the average duration of response was just under six months.

Before receiving Botox, patients should be checked for other causes of the sweating problem, such as an overactive thyroid, to avoid Botox treatment masking a potentially serious disease, FDA cautioned.

Side effects include injection site pain and bleeding, sweating in other parts of the body, flu-like symptoms, headache, fever, itching and anxiety, FDA said.

Dermatologists have long offered Botox to hyperhidrosis sufferers, but FDA approval means maker Allergan Inc. now can advertise the use. Allergan says price varies geographically but the average cost is $750 for both arms.