In the past 50 years, there have been few changes in male contraception compared to the range of options available to women. Today, the only contraceptive methods available to men are:
- condoms - a form of barrier contraception that stops sperm from reaching and fertilising an egg
- vasectomy - a minor surgical procedure that stops sperm from being ejaculated from a man's penis during sex (it is usually permanent)
Some men use withdrawal to try to prevent pregnancy, when they pull their penis out of their partner's vagina before ejaculating. However, this is not a recommended method of contraception. Sperm can be released from the penis before ejaculation.
Types of research
There are two main areas of research into male contraception:
- hormonal contraception - where synthetic hormones are used to temporarily stop the development of healthy sperm
- non-hormonal methods - where other techniques are used to stop healthy sperm from entering a woman’s vagina
These are explained further below.
In fertile men, new sperm cells are constantly created in the testicles. This process is triggered by the hormone testosterone.
The goal of hormonal contraception research is to find a way of temporarily blocking the effects of testosterone so that the testicles stop producing healthy sperm cells. However, this needs to be achieved without lowering testosterone levels to such an extent that it triggers side effects, such as a loss of sexual desire.
Synthetic testosterone and other steroid combinations
One way of doing this is by giving men a synthetic version of testosterone, together with a hormone called progestogen. Progestogens are synthetic versions of a female sex hormone often found in female hormonal contraceptives, such as the progestogen-only pill.
This approach stops the testes producing testosterone which, in most cases, prevents normal sperm production. However, at the same time it keeps the amount of testosterone in the blood normal, preventing side effects.
This is a very effective approach, but some men still carry on producing enough sperm to cause a pregnancy. The reason why this happens is unknown, but it may be that some men carry on producing enough testosterone to continue to stimulate some sperm production.
Research is now focusing on different combinations of synthetic testosterone and progestogens. Several trials in different countries are looking at the effectiveness and long-term safety of hormonal contraceptives for men, including some phase III trials. Phase III trials are the last clinical trials carried out before a medicine is given a marketing licence.
An important disadvantage of using synthetic testosterone is that sperm production is suppressed at different rates in men of different ethnic origins.
These differences may be due to genetic, dietary or environmental factors, but the exact reasons are unknown. Understanding the reasons may lead to new ways of providing effective contraception for all men of diverse ethnic backgrounds.
Many of the non-hormonal methods of contraception currently being studied involve the vas deferens. The vas deferens is the tube that sperm pass through on their way to the penis. This tube is cut during a vasectomy.
RISUG and the IVD
One promising avenue of research is a technique called Reversible Inhibition of Sperm Under Guidance (RISUG). During this technique, a non-toxic synthetic chemical is injected into the vas deferens. The chemical reacts and blocks the vas deferens. The chemical also kills sperm when they come into contact with it. The chemical is effective almost immediately after it is injected.
The chemical stays in place until a man decides that he wants to have children. It can then be washed out using another injection which dissolves it and flushes it out of the vas deferens.
A variation of this technique is the intra-vas device (IVD). It involves injecting a "plug" into the vas deferens which can be removed later. The IVD filters out the sperm as it passes though the vas deferens.
Initial results of RISUG and IVD are promising, but further research is needed to assess the long-term effectiveness and safety of both techniques.
Reasearch published in 2013 found that blocking certain proteins in the bodies of male mice rendered them infertile, but did not affect their sexual behaviour or the quality of their sperm. It prevented the sperm cells from being launched during ejaculation. When the mice's sperm was used to artificially inseminate female mice, it resulted in pregnancies and healthy baby mice.
If a way can be found to block these proteins in human males, this may take research a step closer to producing a male contraceptive pill. However, the research is in the very early stages and a male pill has not been developed.
Other research is focusing on the epididymis. The epididymis is a long, coiled tube behind the testicles that stores and helps transport sperm.
Attempts have been made to interfere with the way that the sperm matures inside the epididymis and to interfere with the way that the epididymis works. However, so far neither approach has been successful.
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