Vomiting, Diarrhoea and the Pill
When a dose does not count — the three-hour rule for vomiting, the 24-hour threshold for diarrhoea, and what to do through a stomach bug.
Part of the Complete Contraception Guide.
Key fact: Three hours is the number. Vomit within three hours of taking a pill and the dose may not have been absorbed — treat it as a missed pill. Vomit later than that and there is nothing to replace.
The three-hour rule
A pill has to be absorbed to work, and absorption from the small intestine is essentially complete within about three hours of swallowing it. That gives a clean rule.
| You vomit… | What it means | What to do |
|---|---|---|
| Within 3 hours of taking the pill | The dose may not have been absorbed | Take another pill from a spare strip if you can keep it down. If you cannot, treat it as a missed pill |
| More than 3 hours after taking it | The dose is absorbed | Nothing. Carry on as normal |
If you replace the pill successfully, your pack finishes a day early, which is expected and not a problem. If you cannot keep anything down, the missed-pill rules take over: one dose lost from a combined pill needs nothing extra, two or more within 72 hours needs seven days of condoms and a check on where you are in the pack.
What counts as severe diarrhoea
Diarrhoea is less clear-cut than vomiting, because mild loose stools do not prevent absorption. The threshold in UK guidance is severe diarrhoea lasting more than 24 hours — at that point, treat the pills taken during it as missed and use additional precautions.
- One or two loose stools: no action needed
- Severe diarrhoea for under 24 hours: keep taking your pills at the usual time; no extra precautions
- Severe diarrhoea for more than 24 hours: keep taking the pills, and use condoms until you have had seven days of correct pill-taking after it settles — 48 hours if you are on a desogestrel mini pill
"Severe" is doing real work in that sentence. It means frequent, watery stools of the kind that come with a genuine gastrointestinal infection, not a single upset after a takeaway.
If you are on the mini pill
The same three-hour principle applies. Take another pill if you can, and if not, follow the mini pill rules: take one as soon as you can keep it down, carry on as normal, and use condoms for 48 hours from restarting correct pill-taking. Emergency contraception is worth considering if you had unprotected sex from the point the dose was lost until 48 hours after resuming.
Both mini pills supplied here, Zelleta and Cerazette, are desogestrel, so 48 hours is the figure that applies rather than the longer combined-pill window.
If you were sick after emergency contraception
Vomiting within three hours of either emergency contraceptive tablet means the dose may be lost and another dose is needed. This matters more than a lost contraceptive pill, because there is no second chance later in the cycle. Contact a pharmacist or prescriber the same day rather than waiting to see what happens.
Nausea is a recognised effect of both tablets, so if you are prone to it, taking the dose with food helps. Emergency contraception compared covers the timing windows that determine which option is still available to you.
A stomach bug lasting several days
Norovirus and similar infections can run for two or three days, and that is long enough to lose cover on an oral method. The approach is straightforward:
1
Keep taking your pills
At the usual time, even if you are not confident they are staying down. There is no benefit to stopping.
2
Use condoms, or avoid sex, until it has passed
And for seven days of correct pill-taking afterwards on a combined pill, or 48 hours on a mini pill.
3
If you are on a combined pill in the last week of the pack
Skip the break and go straight into the next pack, exactly as you would after missing pills in week 3.
4
Consider emergency contraception
If you had unprotected sex during the illness, or in the days just before it.
Anti-sickness and anti-diarrhoeal medicines do not restore the lost doses, though they may help you keep the next one down. Some products, including activated charcoal, can interfere with absorption if taken at the same time as your pill — separate them by a few hours.
If it keeps happening
Repeated vomiting or chronic diarrhoea makes an oral contraceptive unreliable in a way no set of rules can fix. Situations where this comes up regularly:
- Morning sickness in a subsequent pregnancy — a different problem, but the same absorption issue
- Migraine with vomiting, where attacks are frequent
- Crohn's disease, ulcerative colitis or coeliac disease with active symptoms
- After bariatric surgery, particularly procedures that bypass part of the small intestine — oral contraception may be less reliable regardless of symptoms
- Bulimia, or any pattern of regular vomiting
In all of these, guidance points towards a non-oral method rather than towards better adherence.
Options that bypass the stomach
| Method | Why it helps here |
|---|---|
| Implant | Three years, absorbed under the skin, unaffected by gut symptoms |
| Injection | Every 12 to 13 weeks, and also unaffected by enzyme-inducing medicines |
| Hormonal coil | Five to eight years, acts locally, often lighter periods |
| Copper coil | Hormone-free, five to ten years, unaffected by anything you swallow |
| Patch or ring | Oestrogen-containing, so the same restrictions as the combined pill apply — but absorption does not depend on the gut |
The comparison of contraceptive options sets these out in more detail, and the contraception overview covers effectiveness in typical use.
What does not affect absorption
- Feeling nauseous without vomiting. Nausea alone does not stop absorption. It is also a common early effect of the combined pill that usually settles.
- Vomiting more than three hours afterwards, however unpleasant.
- Mild loose stools, or a single episode of diarrhoea.
- Heartburn, indigestion or reflux. No effect on the pill.
- Taking the pill with or without food. Either is fine; food can reduce nausea.
- Alcohol. It does not reduce the pill's effectiveness — but being sick after drinking follows the same three-hour rule as any other vomiting.
A practical habit: keep a spare strip. Being able to replace a vomited pill within the hour turns a lost dose into a non-event, and it is the single most useful thing to have on hand if you are prone to migraine or travel sickness.
Frequently Asked Questions
I was sick after taking my pill. Do I need to take another?
If you vomited within three hours of taking it, take another pill from a spare strip. Beyond three hours the dose has been absorbed and there is nothing to replace. If you cannot keep a replacement down, follow the missed-pill rules for your pill type.
Does diarrhoea stop the pill from working?
Only if it is severe and lasts more than 24 hours. Mild or brief diarrhoea does not prevent absorption. With severe diarrhoea beyond 24 hours, keep taking your pills and use condoms until you have had seven days of correct pill-taking afterwards, or 48 hours on a desogestrel mini pill.
Should I stop taking the pill while I have a stomach bug?
No. Keep taking your pills at the usual time throughout, and use condoms during the illness and for the days afterwards. If you are on a combined pill and reach the end of the pack, skip the break and start the next pack straight away.
I vomited after taking the morning after pill. What now?
If it was within three hours, the dose may be lost and another dose is needed. Contact a pharmacist or prescriber the same day, because there is no later opportunity in that cycle. Beyond three hours no repeat is needed.
Does alcohol affect the pill?
Alcohol does not reduce the pill's effectiveness. The risk is indirect: being sick within three hours of taking a pill means the dose may be lost, and drinking makes forgetting a dose more likely.
References
- Faculty of Sexual & Reproductive Healthcare. Combined Hormonal Contraception (amended October 2023). fsrh.org
- Faculty of Sexual & Reproductive Healthcare. Progestogen-only Pills (August 2022, amended 2026). fsrh.org
- Faculty of Sexual & Reproductive Healthcare. Emergency Contraception (March 2017, amended 2026). fsrh.org
- Faculty of Sexual & Reproductive Healthcare. Drug Interactions with Hormonal Contraception (May 2022). fsrh.org
- Faculty of Sexual & Reproductive Healthcare. Problematic Bleeding with Hormonal Contraception. fsrh.org
- Faculty of Sexual & Reproductive Healthcare. UK Medical Eligibility Criteria for Contraceptive Use (UKMEC 2025). fsrh.org
- NHS. Contraception. nhs.uk
Medical disclaimer: This article is for informational purposes only and does not constitute medical advice. Contraceptive choice depends on your medical history, and no method described here protects against sexually transmitted infections. Always read the leaflet supplied with your own pill and consult a qualified healthcare professional. In a medical emergency, call 999.