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When I tell people

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that I'm trying to develop
a contraceptive pill for men,

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the response usually varies
along gender lines.

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Women say something like,

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"Fantastic. It's about time. When?"

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(Laughter)

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Men have one of two responses.

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They either love the idea,

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or they look at me a little warily

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and wonder what exactly
I have in store for their testicles.

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(Laughter)

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So why does the world need a male pill?

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Well, what if I told you

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that of the six million pregnancies
annually in the United States,

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three million of them are unintended?

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That's half.

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That's a really surprising number.

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And those three million
unintended pregnancies

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account for the vast majority
of the more than one million abortions

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annually performed in the United States.

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Happily, the rate of unintended pregnancy
has fallen in the last few years

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by about 10 percent.

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This is because more women
are using effective, long-acting,

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reversible forms of contraception.

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But we still have a long way to go.

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One approach that's finally
becoming a real possibility

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is better contraceptive options for men.

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Think about it.

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We have over a dozen methods
of contraception for women:

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pills, patches, IUDs,
shots, sponges, rings, etc.

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For men, we've had the same two options

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for more than a hundred years:

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condoms and vasectomy.

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Despite having only two options,

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both of which have significant drawbacks,

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men currently account
for 30 percent of all contraceptive use,

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with 10 percent of couples
relying on vasectomy

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and 20 percent of couples using condoms.

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Why are 20 percent of couples
relying on condoms for contraception

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when condoms have a one-year
failure rate of over 15 percent?

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It's because many women
can't either safely take

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currently available female contraceptives,
for reasons such as blood clots,

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or they can't tolerate the side effects.

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So if we think a male contraceptive
would be useful, the next question is:

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How do we go about developing one?

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Well, there's two general approaches.

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The first approach is to try and interfere

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with the way the sperm
swim towards or bind to the egg.

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This approach turns out
to be really difficult,

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because it's hard to get enough medication
in the small volume of the ejaculate

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and have it still work inside
the female reproductive tract.

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This is why there's been a lot more work
done on the second approach,

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which is turning off
sperm production entirely.

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This is also challenging.

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Why? Turns out
that men make a lot of sperm.

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(Laughter)

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Men make a thousand sperm every second

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and to have an effective contraceptive,

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you need to get that level
of sperm production

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down to one percent of its normal value.

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The good news is, this is possible,

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almost.

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The most studied approach has been to use
hormones to suppress sperm production.

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Testosterone and progesterone,
when administered together,

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will suppress the signals from the brain
to the testes to make sperm,

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and in about 90 percent of men,

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sperm production after
three to four months will stop.

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Unfortunately, 10 percent of men
don't respond to these hormonal regimens

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for reasons that aren't understood.

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For the last several years,
my colleagues and I

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have been taking a different approach
to male contraceptive development,

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one that doesn't involve
the administration of hormones.

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Specifically, we are looking to block
the function of vitamin A in the testes.

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Why? Well, for over 90 years
it's been known

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that you need vitamin A to make sperm.

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Animals who are deprived
of vitamin A in their diet

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stop making sperm

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and restart making sperm again
when the vitamin A is reintroduced.

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The vitamin A that we ingest

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is converted by a family of enzymes
to something called retinoic acid.

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One of these enzymes
is found only in the testes.

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It's this enzyme
that we are attempting to block.

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The blockade of this enzyme
should deprive the testes of retinoic acid

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and stop sperm production

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without affecting vitamin A's functions
elsewhere in the body.

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We're testing this approach in animals

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and hope to move to human testing soon.

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Obviously, the impact
of such a male contraceptive

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would go well beyond reproductive biology.

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It's interesting to speculate
about the effect that it would have

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on relationships between men and women.

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One intriguing possibility

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is that a man could monitor
his contraceptive status over time.

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In the last several years,

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two groups have introduced
home sperm-testing devices

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that are iPhone-based

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and that are easy to use.

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A man could test his sperm count
and share the result with his partner.

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If the man's sperm count were zero,

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the man and his partner
would feel very comfortable

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relying on his contraceptive.

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A tool like this,
coupled with a male contraceptive,

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could greatly increase the role for men
in preventing unintended pregnancy.

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The researchers who are working
on male contraception

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are trying to create
a better future for couples,

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a future where contraception is no longer
considered just "a woman's issue,"

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rather an issue
for couples to decide together.

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So why does the world need a male pill?

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Well, I believe that a male pill

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will help reduce the stubbornly high
rates of unintended pregnancy and abortion

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and allow men to equally participate

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in contraception.

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Thank you.

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(Applause)