References UK clinical guidance from the NHS, the British HIV Association (BHIVA), and the British Association for Sexual Health and HIV (BASHH). Last updated: April 2026.
The contraceptive pill’s effectiveness depends on when in your cycle you start taking it. In some cases, it works from day one. In others, you need to use extra protection for the first 7 days. The exact timing depends on which type of pill you’re taking and where you are in your menstrual cycle when you start.
Here’s a practical guide.
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Combined Pill (Oestrogen + Progestogen)
| When You Start | When It Works |
|---|---|
| Day 1 of your period | Immediately |
| Within first 5 days of period | Immediately |
| Any other time | After 7 days of correct use — use condoms in the meantime |
Progestogen-Only Pill (Mini Pill)
| When You Start | When It Works |
|---|---|
| Day 1 of your period | Immediately |
| Within first 5 days of period | Immediately |
| Any other time | After 2 days of correct use — use condoms in the meantime |
Switching Between Methods
If you’re switching from another method:
- From one pill to another — usually effective immediately if taken correctly
- From the implant or coil — take the new pill on the day the old method is removed
- From no contraception — follow the standard start rules above
After Childbirth
- Combined pill — can start at 21-28 days after birth if not breastfeeding
- Progestogen-only pill — can start immediately after birth, including if breastfeeding
If starting after day 21, use condoms for the first 7 days of combined pill or 2 days of progestogen-only pill.
After Miscarriage or Abortion
You can usually start either type of pill immediately or within 5 days. After this, use backup for the relevant number of days.
What Counts as “Correct Use”
- Take one pill at the same time every day
- Combined pill: follow the pack instructions (typically 21 days on, 7 days off, or continuous)
- Progestogen-only pill: no break, one every day
- If you vomit within 3 hours of taking a pill, it may not have been absorbed
- Severe diarrhoea can also affect absorption
What Reduces Pill Effectiveness
- Missed pills
- Vomiting or severe diarrhoea
- Some antibiotics (rifampicin, rifabutin — not most others)
- Some anti-epileptic drugs
- St John’s Wort
- Some HIV medications
If you’re on any regular medication, tell your GP or contraception provider so they can advise.
Missed Pills
If you miss a pill, the advice depends on the type:
- Combined pill — if over 24 hours late, follow the missed pill instructions in your packet
- Progestogen-only pill — if over 3 hours late (or 12 hours for some brands), follow missed pill instructions
When in doubt, use condoms and speak to a clinician.
Read more: Avoiding STIs | Menstrual health and HIV | What is chlamydia?
Frequently Asked Questions
Does the pill protect against STIs?
No. The pill only prevents pregnancy. Use condoms for STI protection.
What if I’m not sure I started correctly?
Use condoms as backup and speak to your GP or contraception provider. Better safe than sorry.
Do antibiotics affect the pill?
Most antibiotics don’t affect pill effectiveness. Only rifampicin and rifabutin significantly interact. However, if you’re ill with vomiting or diarrhoea from the infection, that can reduce absorption.
Related reading
- Blood Test for Syphilis, Hepatitis B and Hepatitis C
- Can You Get an STI From Being Fingered?
- Can You Catch an STI From a Toilet Seat?
- Can You Clear HPV Once You Have It?
- Can You Die From Hepatitis B?
Sources
- NHS — Sexual health conditions
- BASHH — UK clinical guidelines for STI management
- British HIV Association (BHIVA) — HIV treatment guidelines
- Terrence Higgins Trust — sexual health information
- UK Health Security Agency — STI surveillance data
Steve Page is a recognised expert on Sexually Transmitted Diseases (STDs) and STD treatments, having published numerous articles in peer-reviewed journals and presented his research at conferences around the world. He has an in-depth understanding of the latest medical research on STDs, and is an advocate for the development of new treatments and protocols to improve the health of those affected. In addition to his research, he has dedicated his career to understanding the causes and symptoms of STDs, as well as how to best treat those impacted.
