Botox isn't just for wrinkles any more. It can also help women with urinary incontinence lead a more normal life.

The largest study to date has found botulinum toxin (Botox) effective at calming the overactive bladders of women with urinary incontinence that had not responded to standard treatments. One Botox treatment was good for six months.

Standard treatments include pelvic floor muscle exercises to improve muscle control and anticholinergic medication, which may lower the activity of nerves that cause the bladder muscle to contract.

Nearly one-third of the women who received Botox had full control over their urination six months after treatment.

The treatment can have side effects. One of six women in the study reported difficulty urinating at some point during the six months. And urinary infections also rose in women who received Botox. But the treatment helped far more women than it caused these problems for.

A common cause of urinary incontinence is an overactive bladder muscle whose contraction isn't fully under a person's control. Standard treatments include pelvic floor muscle exercises to improve muscle control and anticholinergic medication, which may lower the activity of nerves that cause the bladder muscle to contract. While these treatments do help many sufferers, they don't help everyone. And the medication can cause side effects including constipation, dry mouth and blurred vision.

The women in the study all had severe muscle-related bladder problems that had not improved after eight weeks of conventional treatment.

Over four years, the RELAX study recruited 240 such women from eight UK hospitals. A total of 122 received injections of 200 International Units (IU) of botulinum toxin, 20 IU each at 10 different sites in the bladder wall, while 118 received 10 injections of saline. The women reported on how the treatment was working six weeks, three months and six months after treatment.

Thirty-one percent of the women who received Botox reported being fully continent six months afterward, compared to 12% who received saline injections. And even those who did not become fully continent reported benefits: on average, leakage episodes decreased from 6.0 to 1.67 per day.

The most common side effects were urinary tract infection and difficulty urinating. Urinary tract infection occurred in three times as many women who received Botox as in those who received saline (36 women to 12). And four times as many women who received Botox had enough difficulty urinating to require occasional self-catheterization, (16 women to 4).

It's possible that these side effects can be reduced by altering the initial dosage of Botox; this is a fairly new procedure.

Self-catheterization requires learning how to insert a plastic or rubber tube into the urethra to collect the urine, a procedure which can be inconvenient. But most of the women in the study who had to resort to it found it preferable to their pre-study state of affairs. And those who had no such need were delighted at the improvement the treatment made to their everyday lives.

An article on the study was published online by European Urology and is freely available.