Researchers believe they are moving closer to creating the world's first birth control pill for men, after identifying ways to make a number of promising drug candidates more suitable for the job.

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Researchers say they are making progress toward the development of a male birth control pill.

Lead researcher Gunda I. Georg, PhD, of the University of Minnesota College of Pharmacy, and colleagues recently presented their findings at the 251st National Meeting & Exposition of the American Chemical Society (ACS) in San Diego, CA.

For years, researchers have been striving to develop a contraceptive pill for men. Some studies have investigated the male hormone testosterone as a possible basis for such a drug; it can cause infertility at specific doses.

"But at those doses, it doesn't work for up to 20% of men, and it can cause side effects, including weight gain and a decrease in 'good' cholesterol," notes Jillian Kyzer, a graduate student at Minnesota and coauthor of the new research.

Other compounds have been assessed as a male contraceptive pill, but Georg and her team note there are a number of barriers that need to be overcome before such a drug can reach the market.

The pill would need to be soluble - allowing it to be taken orally - and it would need to work quite quickly, without affecting a man's sex drive.

What is more, men would need to be able to use the pill safely for a long time - even decades - and the effects on fertility would need to be reversible, with no negative impact on sperm or embryos, in the event users want to start a family.

"That's a very high bar for bringing a male contraceptive to market," notes Georg.

Making progress by tweaking structure of chemical compounds

Some pharmaceutical companies have reached experimental stages for a male birth control pill, but Georg and colleagues note that some serious flaws persist.

The team speaks of one experimental compound that, while soluble, is unable to selectively target the cells required to temporarily inhibit male fertility; the compound interacts with retinoic acid receptor-α (RAR-α) - a protein involved in male fertility - as well as two other retinoic acid receptors not associated with male fertility, meaning the compound could cause adverse side effects.

For their research, Georg and her team are developing a number of compounds that are similar to the one described, in terms of chemical structure. However, they have discovered that making certain "tweaks" to the compounds can improve their suitability as a male contraceptive pill.

While investigating one compound that interacts with RAR-α, for example, they found that replacing an amide bond, or peptide bond, with ones that are known to mimic amide bonds improved the stability of the compound, meaning it would work for longer in the body.

However, replacing these bonds also lowered the ability of the compound to selectively target RAR-α.

Still, the researchers believe they are making progress toward developing a male birth control pill, and they are continuing to tweak their compounds in order to achieve "the ultimate balance of solubility, specificity and stability."

While there are a number of birth control pills available for women, they are not a suitable option for all couples. Georg says:

"It would be wonderful to provide couples with a safe alternative because some women cannot take birth control pills."

Earlier this year, Medical News Today reported on a study that found - contrary to previous research - oral contraceptive use is "unlikely" to cause birth defects.