NEW YORK — This week the National Institutes of Health (NIH) announced the start of a trial for a male contraceptive in gel form. It's a big step in the search for a birth control men can use, and if it works, it would fill an important public health need.

According to the NIH, the gel called NES/T, contains a form of progestin, a hormone that can prevent ovulation during pregnancy. It blocks natural testosterone, reducing sperm production. The gel also contains replacement testosterone to maintain normal sex drive and other functions.

It's applied to the back and shoulders daily and is absorbed through the skin. Researchers will study around 420 couples for about a year to see if the gel is effective in preventing pregnancy. But CBS News medical contributor Dr. Tara Narula said it won't be available for use right away. Since it's a first trial, more research will be needed down the road.

"For any product like this to move forward, it's going to have to be safe, effective and reversible," Narula said.

Right now, there's no male birth control pill available. Narula said one reason is because a lot of the research has been left to non-profits and governments. Another issue comes down to biology.

"It's much harder to repress the production of hundreds of millions of sperm that are produced every day versus one to two eggs produced every month," Dr. Narula said. "But researchers are saying look, it's time for gender equity right now. We need to have more shared responsibility in family planning."