Each drug is different. But they all work by relaxing the bladder muscle, reducing spasms that can cause urgency and leakage.
The new review is based on data from 94 studies that compared at least one of the medications to a placebo pill.
As a group, the drugs all helped women achieve continence more frequently than placebo pills. The researchers estimate that for every 1,000 women who were treated with the drugs, less than 200, or 20%, achieved continence on the medications.
But side effects were also common.
"One of the things we report is that 50% of the women in the study stopped treatment with the drugs within one year," says researcher Robert L. Kane, MD, a professor of long-term care and aging at the University of Minnesota?s School of Public Health in Minneapolis. "Basically, it's because of side effects."
The review does not make recommendations about the use of these drugs.
"It turns out that it's as important to sit down with your doctor and look at the side effect pattern of the pills as it is the direct effects," Kane says, "because for the most part, a number of them basically have about the same effectiveness, but they have different patterns of side effects."