The coil, the pill and what you lose

The question is usually asked about performance. That is the wrong question, because the honest answer to it is that any group-level effect is most likely trivial. The right question is what happens to the one measurement you were getting for free.

Before anything else: which method a woman uses is a medical decision made with a doctor, for reasons that have nothing to do with sport.

Nothing on this page is a reason to choose one, change one or stop one.

How common this is

Reported prevalence in female athletes varies considerably by sport and by study, with figures across the literature ranging from roughly a third to around two thirds.

So in any group of female fighters, a substantial share are using something. This is not a niche question and it should not be an awkward one.

What the performance research found

A systematic review and meta-analysis examined oral contraceptive pills and exercise performance, comparing users with naturally menstruating women, and also comparing the pill-taking days with the withdrawal days.

The conclusion: use might result in slightly inferior performance on average, but any group-level effect is most likely trivial.

Which is, you will notice, the same shape of answer as the research on cycle phase itself. Small average effects, large individual variation, and no basis for a general rule.

A 2025 study looked directly at muscle protein synthesis and found that oral contraceptive phase did not influence it at rest or in response to resistance exercise.

The distinction that actually matters

Not pill against coil. Intermittent against continuous.

A woman on a standard combined pill still has a monthly bleed during the break, though it is a withdrawal bleed rather than a true menstrual period.

A woman with a hormonal coil frequently has lighter bleeding or none at all, and that is an expected effect of the method rather than a problem with it.

What that costs you, specifically

The point of this article.

The cycle matters to a fighter because menstrual function responds to energy availability, which makes it a free early warning that a body is not getting enough. Performance scheduling is a much weaker reason.

Continuous methods remove that reading. If you have a coil and your bleeding stopped, you cannot tell the difference between the coil working as intended and a camp that has pushed you into low energy availability.

The signal is gone, and it was the most useful one you had.

Keep the coil if it suits you, and replace what it took away.

What to monitor instead

Everything below applies to anyone, but it becomes necessary rather than optional when the cycle is not readable.

Energy availability, calculated rather than guessed. The free calculator gives you the number in about a minute. Run it at the start of camp and again when volume peaks, because that is when it falls without anyone changing what they eat.

An output measure you can repeat. A jump, a sprint, a lift you know your numbers on. Taken monthly, it catches decline you cannot feel.

Resting heart rate on waking, same time, several days running.

Iron status by blood test, because the symptoms overlap with under-fuelling and neither can be identified by feel.

Bone, if there is any history of stress injury. That belongs in front of a physician together with your training history.

The evidence gap worth knowing about

An audit of the exercise performance literature examined how hormonal contraceptive users are represented in it. The picture is not good: many studies exclude them, and many that include them do not report which method was used.

Given that a large share of female athletes use something, that means a substantial part of the research on female athletes was conducted on a subgroup, or on a mixed group whose composition is unknown.

So when somebody quotes you a confident number about women and performance, it is fair to ask which women.

Anti-doping

Hormonal contraceptives are not on the Prohibited List. This comes up more often than it should, usually from fighters who have heard that anything hormonal is a problem.

It is not, and no exemption is required. As always, confirm the programme governing your bout, and if you are ever prescribed something else, check that specific medication rather than assuming.

What I would say in a consultation

If a fighter tells me she has a coil and no longer bleeds, I do not treat it as a red flag. It is an expected effect of a method she chose with a doctor.

What I do is write down that we have lost a monitoring tool, and build the replacements in deliberately. Energy availability calculated at 2 points in every camp, one repeatable output measure, and a ferritin test at the start rather than in week six.

That takes about 20 minutes a camp to set up. It is not a burden, and it fills a gap that otherwise sits there unnoticed until something breaks.