Using testosterone doesn’t make Viagra work better.

Using a testosterone gel in addition to Viagra doesn't make the little blue pill work any better, according to a US study.

Studies have suggested that about one-quarter to one-third of men with erectile dysfunction, or ED, also have low testosterone, and the authors of the study - which appeared in the Annals of Internal Medicine - say that a starting course of sildenafil citrate, marketed as Viagra, helped improve sexual function for men with both conditions.

But adding testosterone, typically prescribed to men who have both low testosterone levels and symptoms such as little interest in sex or low muscle and bone mass, on top of Viagra, doesn't provide any added sexual benefits, said lead author Matthew Spitzer, from the Boston University School of Medicine.

"Sildenafil plus testosterone was not superior to sildenafil plus placebo in improving erectile function in men with erectile dysfunction and low testosterone levels," Spitzer and his colleagues wrote.

The study included 140 men, aged 40 to 70. All were prescribed Viagra at 50 or 100 milligrams, which they took as needed before sex. After three to seven weeks, half of the men were randomly assigned to also use a daily testosterone gel, and the other half used a drug-free placebo gel.

During the Viagra-only portion of the study, men's erectile function scores improved.

On the sexual functioning scale, a score of 11-16 is considered "moderate" erectile dysfunction and 17-21 is "mild to moderate" dysfunction. The highest possible score, signaling no erectile problems, is a 30.

On average, men's scores increased from 12.1 to 19.8 with Viagra. Their testosterone levels also rose.

For men who were then given the testosterone gel, testosterone levels increased significantly again. But neither those men nor the ones who used the placebo gel had any further change in their erectile function over the next three months.

There was also no difference between the two groups on measures of sexual desire, orgasm and frequency of intercourse.

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