According to Memory-alpha, Contraception injection:

In The Making of Star Trek, it is stated that the birth control practiced on board the USS Enterprise was never discussed in any episode of The Original Series because the censors would not have allowed it. But if it were to have been discussed, they would have explained contraception to be based on monthly injections mandatory for unmarried women and voluntary for married women. If a member of the crew became pregnant, she would have a choice between medical discharge or rotation to a shore base for the duration of the pregnancy. (pages 206, 207)

Yet, when Benjamin Sisko and Kasidy Yates become pregnant they are surprised. Sisko forgot to renew his injection.

Why would Kasidy Yates have relied exclusively on Sisko's injections? Has the responsibility shifted from women to men since TOS time? Are civilians not allowed access to birth control?

Why haven't they developed something more reliable?

How exactly does birth control work in Star Trek?

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    Hmm... Obviously I'm not sure how to word this question properly. Note that I don't consider memory-alpha to be canon, I had this question without the quote from there.
    – Daniel
    Commented Oct 16, 2015 at 2:22
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    memory alpha is a fairly valid source, especially when they cite specific episode. which this article does... you essentially linked a sourced answer
    – Himarm
    Commented Oct 16, 2015 at 2:34
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    @Himarm What I linked doesn't answer my question at all, it's just the only relevant information I found when I searched on the topic.
    – Daniel
    Commented Oct 16, 2015 at 2:37
  • that most likely the only episode with it included >.>
    – Himarm
    Commented Oct 16, 2015 at 2:39
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    While I don't agree about "Memory Alpha" not being canon -- Memory Alpha contains many useful canonical references -- I do agree that The Making of Star Trek is not canon for anything that never actually made it to the screen, no matter how authoritative the source. However...therein lies the real problem. Sisko forgetting to get his injection is the very first time birth control is mentioned in ANY canonical context, leaving your question completely unanswerable from canon sources. Commented Dec 22, 2015 at 19:40

2 Answers 2


Birth control works quite well in the Star Trek universe, thank you for asking!

It seems that you are asking three separate questions:

  1. Why Sisko was getting birth control injections could be explained simply that Yates was allergic to whatever birth control medications are available in the Trek universe.
  2. Should birth control of the future be more reliable than the present? In real life, if a woman is on the pill and a male uses condoms there is still a very small chance of pregnancy.
  3. You answered the question when you asked if birth control in the Star Trek universe is a renewable contraceptive injection, that in males presumably somehow inhibits sperm cell reproduction. I would assume in females works about the same way that modern day birth control injections do.
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    With regards to #1, Kasidy specifically says "one of us", implying they both get injections.
    – Austin
    Commented Jul 19, 2016 at 7:30
  • “Why Sisko was getting birth control injections could be explained simply that Yates was allergic to whatever birth control medications are available in the Trek universe.” Or, alternatively, simply Sisko was a stand-up guy. Commented Jul 19, 2016 at 9:27
  • I didnt actually rewatch the episode, reading the question I assumed that only Sisko was getting the injections
    – revenant
    Commented Jul 19, 2016 at 11:32
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    The tone of that "one of us" means YOU. Otherwise you'd have to believe that her injection failed while he had forgotten his. Commented Oct 24, 2020 at 0:27
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    Yes, the way Kassidy stated it is the same way I've seen women, after their second or third child, say to their husbands "One of us is getting a vasectomy." The blame was clearly on Sisko. Commented Nov 18, 2020 at 22:28

The simplest explanation based on dialog in the episode, and logic, is that both partners get monthly birth control injections. It may not be strictly required that both partners do, rather, it simply allows for maximum effectiveness.

Based on a quick google, injection-based birth control for women today has a 94-99% effective rate.

Presumably, a male birth control injection will cover the remaining percentage. Meaning if both partners are keeping up to date on their monthly injections, chances of getting pregnant is pretty much 0.

Even with Sisko forgetting his injection, pregnancy was probably still unlikely, but not impossible. Luck just wasn't on their side.

Out of universe, it seems clear that the writers needed a way to get Kasidy pregnant in a realistic way. Given what we know of birth control technology today, a dual partner approach being even more effective (except for simple human error) seems realistic. Given that Sisko is fighting a war, it makes sense he would be the forgetful one.

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