Some women with incontinence problems can improve their condition using approved medications, but a new research review finds that inadequate relief and side effects may prevent many others from benefiting.

The study, published online in the Annals of Internal Medicine, re-examined 94 clinical trials testing drugs for women's urge incontinence - when urine leaks after a sudden, strong urge to urinate.

It's less common than so-called stress incontinence, when urine leaks because of pressure on the bladder from things like exercise, coughing or heavy lifting.

In the U.S., there are several drugs approved to treat urge-type incontinence: fesoterodine (Toviaz), oxybutynin (Ditropan), solifenacin (Vesicare), tolterodine (Detrol) and trospium (Sanctura).

They work by relaxing the bladder and easing the urge to urinate. But that clears up incontinence episodes in only a minority of women, the new review shows.

Researchers found that for every 1,000 women treated with the drugs, only about 85 to 130 saw their incontinence disappear.

Fesoterodine was the most effective drug, and tolterodine the least according to the research.

But overall, the benefit of medication was modest, since most women in the studies remained incontinent, said lead researcher Dr. Tatyana Shamliyan, of the University of Minnesota School of Public Health in Minneapolis.

And that modest effectiveness needs to be balanced against the risk of side effects, Shamliyan said.

She and her colleagues found that for every 1,000 women treated, between 13 and 63 stopped taking their incontinence medication because of side effects. The highest rate was among women on oxybutynin. Dry mouth and constipation are the most common side effects of incontinence medications.

Shamliyan said women should try lifestyle changes and non-drug treatments first. Medication, she said, "should be seen as a treatment option. But they are not magic pills."

One recent study of U.S. adults found that about 53% of women older than 20 said they'd had problems with urinary incontinence in the past year, this was an increase over previous surveys.

Researchers on that study said the increase was partly explained by rising rates of obesity and diabetes; diabetes is thought to contribute for a few reasons -- by causing nerve damage that affects the bladder, and by boosting the body's urine production, for example.

Shamliyan said the relatively small benefits of drug treatment make preventing urinary incontinence even more important. Women can cut their risk, she said, by eating well and exercising to maintain a healthy weight, and by not smoking -- another risk factor for bladder-control problems. There are also conservative treatments, Shamliyan pointed out.

One is "bladder training", tactics like going to the bathroom at fixed times, even if you don't feel like you need to go. Other options includes Kegel exercise, better known as Pelvic Floor Exercises, to strengthen the pelvic muscles that control urination.