Menstrual Cups, Honestly: What Forty-Three Studies Actually Found

A cup collects blood instead of soaking it up, and in the largest review of them leakage was similar to or lower than disposable pads or tampons. That review, published in 2019, gathered 43 studies and 3319 participants — and only three of those 43 were of moderate-to-high quality, a caveat that travels with every number on this page. Four of the studies compared cups directly against pads or tampons, and it was those four that found leakage similar or lower. A pooled 73% of participants (95% confidence interval 59 to 84) wished to carry on using one. So: about as good as what most people already use, on a small pile of mostly weak evidence, and most people who tried one wanted to keep it.

This page is for anyone weighing up whether to try a cup, and for a parent being asked about one. It prints what the research found, including the unflattering parts and the missing ones.

What a cup is, and what 43 studies really bought us

The NHS describes menstrual cups as products that collect the blood rather than absorb it, and says that unlike tampons and most pads they can be washed and used again. That single difference — collect, not absorb; reuse, not replace — is the whole of what makes a cup a different object, and the rest of this page is what happens once you take that difference seriously. The wider line-up of pads, tampons, cups and underwear is laid out side by side in period products explained.

Forty-three studies sounds like a mountain. It is not, and the reviewers said so themselves: only three of the 43 were of moderate-to-high quality. Three thousand three hundred and nineteen people is a decent total, but a decent total assembled out of mostly weak studies is still mostly weak evidence.

So the honest position is neither "cups are proven" nor "there is nothing behind them". The best evidence points one way, and there is less of it than the confidence around cups online would suggest.

Leaking, which is the only question most people actually have

Four of the 43 studies compared a cup directly against disposable pads or tampons for leaking. In those four, leakage with a cup was similar to or lower than with the disposables. Not dramatically better. Not worse.

That is a smaller and more useful claim than "cups do not leak", which nobody has shown and this page will not say. But it answers the fear that sends most people here — that a cup is a riskier bet than what is already in the bag — and on what has been measured, the answer is no.

The other number worth carrying is the one about staying with it. A pooled 73% of participants wished to continue, with a confidence interval running from 59 to 84. That interval is wide because the studies underneath it were small and varied, and a wide interval is information rather than a flaw: somewhere between three in five and five in six wanted to carry on. What went wrong for the rest is not something the review breaks down. Leaks in general, whatever the product, are covered in period leaks.

Every harm the review reported, in full

Most pages summarise this section as "generally safe" and move on. Here is the actual list, in absolute numbers, out of the 3319 people in the whole review.

All five are totals the 2019 review reported across every study it gathered — not rates from one trial. A study that never asked about a harm cannot have found it.

Two things are true of that list at once: it is short, and every line on it is real. Thirteen coil dislodgements is the one people rarely hear about, and the reason to mention a coil to whoever fitted it before starting with a cup — an ordinary conversation, not an alarm. The five cases of toxic shock syndrome get their own section below.

How much a cup holds, and why that is the interesting number

A 2023 review put figures on the different products. Menstrual cup collection basins hold from 8 ml to 37 ml, measured to the suction-release holes rather than to the rim — so the working capacity, not the brim-full capacity. The same review estimates a fully saturated super pad at about 5 ml and a nighttime pad at up to 15 ml, and menstrual disc basins at between 30 ml and 79 ml.

Set that against what a period is. The NHS says you will lose about 20 to 90 ml of blood — about 1 to 5 tablespoons — over a whole period. Read them together and the arithmetic is startling: the larger cups hold, in one go, a fair share of what many people lose in total. That is the real reason cups get emptied less often than pads get changed. It is volume, not virtue.

The same 2023 review is blunt about the gap in all this: no regulations exist regarding period underwear content or capacity, which is why underwear is missing from the numbers above and gets a page of its own in period underwear, honestly. It also notes that neither cup nor disc use has been studied specifically in the context of heavy menstrual bleeding, which matters if that is you.

How long you can leave one in — the number this page does not have

No source this site can cite gives a maximum wear time for a cup, so no number appears here. What exists is the NHS's instruction, the same for a cup as for a tampon: wash your hands, follow the instructions that came with the product, and do not leave it in longer than needed or recommended. "Recommended" means the leaflet in the box, which is where that number genuinely lives.

Toxic shock syndrome is why the instruction exists. The NHS describes it as a rare but life-threatening condition that can happen when using a tampon or a menstrual cup, or from an infected wound. Early symptoms it names: a high temperature or feeling hot, cold or shivery, muscle aches, and a raised skin rash that feels like sandpaper. Call 999 or go to A&E for blue, grey, pale or blotchy skin, a rash that does not fade, difficulty breathing or large areas of peeling skin — and if you are using a tampon or a cup, remove it.

Read that as instructions rather than as a warning about cups in particular: the NHS covers tampons, cups, caps and diaphragms in one breath. The practical version, hand-washing included, is written out in how to use a tampon, and it applies here word for word.

The first month is not the rest of it

There is a learning curve, and for once there is a study that accidentally documents it. A 2025 randomised trial of 20 adults with heavy menstrual bleeding, run across two cycles, had ten people using cups — and eight of those ten had never used one before. The authors flagged that as a limitation of their own results, which is a polite way of describing what most people's first month with a cup is like: fiddly, a bit messy, and not representative of month three.

That cuts both ways. A bad first attempt is not a verdict — and when a study of mostly first-time users reports how a cup performed, the number you are reading has everybody's learning curve baked into it.

A cup is bought once and used again rather than bought again and again, which is a genuinely different shape of spending — although what it is worth in money depends on prices nobody here has checked, and that argument is taken apart in how much does a period cost.

If your periods are heavy, counting emptyings will mislead you

This is the most practical consequence of switching, and it is barely known.

One of the NHS's tests for heavy periods is needing to change a pad or tampon every 1 to 2 hours, or emptying a menstrual cup more often than is recommended. But the 2025 trial found people changed disposable products a mean of 5.5 times a day and emptied cups 3.3 times a day, and its authors concluded plainly that the frequency of emptying a cup is not equivalent to the frequency of changing pads or tampons — so reusable products may lead to heavy menstrual bleeding being missed.

In plain terms: switch to a cup and your changes-a-day number falls without your bleeding changing at all. If that number is the only thing you or a doctor is going on, heavy bleeding can hide inside it. The NHS's other signs do not depend on counting: periods lasting more than 7 days, clots larger than about 2.5 cm, needing two types of product together, bleeding through to your clothes or bedding, avoiding daily activities, or feeling tired or short of breath a lot. Any of those is worth an appointment whatever you are using.

The fix is boring and it works: write it down. The printable period tracker holds your start dates and how many days each period ran — the two facts nobody remembers accurately at a desk. The printable symptom tracker takes the rest: how many times you emptied it, which product you were using, whether anything soaked through. Both are paper and store nothing anywhere. That last column is the small detail that stops a switch to a cup looking, in hindsight, like your periods got lighter.