[b]Dr. Sanjay Gupta]

(CNN) -- When it hit the market four years ago, Viagra was seen as a breakthrough drug for male sexual dysfunction. But a new medication called Melanotan may have some people saying, "Move over Viagra."* But not so fast -- the drug has only been in the early phases of testing for several years now. But researchers have found it can increase the libido of both sexes -- and even promote a good tan.

CNN's medical correspondent, Dr. Sanjay Gupta, joined CNN anchor Bill Hemmer on Tuesday.

HEMMER]
GUPTA]
Same thing happened with Melanotan -- this medication that the University of Arizona originally designed to treat -- to prevent against skin cancer, actually giving you a tan and warding off some of the harmful rays of the skin. Again, patients came in and said, "Look at these secondary effects that we're seeing," and a lot of patients were having those. Certainly they decided to test it, and a big deal it is.

It's now being called the "Barbie drug," and let's hear why. The Barbie drug certainly gives a tan, Bill. ... It also curbs your appetite, you know, you get slim in addition to looking tan, and [it] triggers the sexual process. And we say it that way to distinguish it from Viagra.

This triggers something in the brain. So it actually increases libido, which is very different than the way Viagra works, which just relaxes blood vessels and getting its effects that way. So [it's] almost a different sort of effect and a big deal. Forty-three percent of men in this country have problems with sexual impotence, 31 percent of women. This is a drug that's being marketed at both.

HEMMER] side effects are what?

GUPTA]
A couple of reasons. One is it decreases side effects. No. 2, it actually works a lot quicker. One of the downsides of Viagra -- it took an hour and a half to actually work.

With this medication, it's supposed to work much more quickly. But we're not hearing much more about side effects at this point. It's already been through a couple of trials to show that it's pretty safe.

HEMMER]
GUPTA]
HEMMER]
GUPTA: Well, you know, with the Viagra, it actually worked on the blood vessels only, and this particular medication works on the brain, so it affects your libido for both men and women. So that's why it's being marketed to both.