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Oral contraceptives: what to be careful with
Oral contraceptives prevent pregnancy, mainly by preventing ovulation and by changing cervical mucus and the lining of the womb.
General information only, and not exhaustive. This is not medical advice, not a full list of interactions, and not a reason to start, stop or change a medicine. Interactions depend on the exact drug, the dose, your other medicines and your own health — a pharmacist or doctor is the one who decides. Always read the leaflet that came with your medicine, and ask your pharmacist before adding anything, including supplements.
Group, not a brandATC G03A
Examples in this group: combined oestrogen and progestogen pills; progestogen-only pills. Interactions usually belong to the whole group, but your own leaflet is brand-specific — always the final word.
Food and drink to be careful with
- St John's wort. The clearest supplement interaction here. It induces the liver enzymes that clear these hormones, lowering the level and, with it, the contraceptive protection. It is named explicitly in the leaflets.
- Vomiting and severe diarrhoea. Not a food interaction as such, but the everyday one: if the tablet does not stay in long enough to be absorbed, it may not have worked. Leaflets give specific instructions for how long counts and what to do.
- Grapefruit juice. Raises ethinylestradiol levels modestly. It is described in the literature but is not the reason contraception usually fails.
- Activated charcoal and some binding products. Taken close to the pill, they can reduce absorption.
Timing around meals
Taken at the same time each day. Progestogen-only pills are the more time-sensitive of the two; the window that counts is stated in the leaflet for the specific product.
Alcohol
No direct interaction with the hormones. The practical link is indirect: heavy drinking makes a missed pill and a missed replacement more likely, and vomiting after drinking can mean a dose was not absorbed.
Other things to watch
- Enzyme-inducing medicines — rifampicin, several anti-epileptics, some HIV treatments — reduce effectiveness and usually mean a different contraceptive method is chosen.
- Most antibiotics do NOT reduce the effectiveness of modern combined pills, contrary to long-standing belief; rifampicin and rifabutin are the exceptions.
- Smoking with a combined pill raises clot risk substantially, particularly over the age of 35.
If anything here does not match what you were told, or you notice a new symptom after starting a medicine, contact your pharmacist or doctor — do not just stop taking it. Stopping some medicines suddenly is more dangerous than any food interaction.
Source: The product's own Summary of Product Characteristics and patient information leaflet, published per medicine by the licensing authority. The St John's wort and enzyme-inducer warnings are standing entries in combined oral contraceptive product information. · checked 2026-09-02
Frequently asked questions
What should I avoid with oral contraceptives?
St John's wort is the one people ask about most: The clearest supplement interaction here. It induces the liver enzymes that clear these hormones, lowering the level and, with it, the contraceptive protection. It is named explicitly in the leaflets. This is general information — your leaflet and pharmacist have the specifics.
Can I drink alcohol with oral contraceptives?
No direct interaction with the hormones. The practical link is indirect: heavy drinking makes a missed pill and a missed replacement more likely, and vomiting after drinking can mean a dose was not absorbed.
Should oral contraceptives be taken with food?
Taken at the same time each day. Progestogen-only pills are the more time-sensitive of the two; the window that counts is stated in the leaflet for the specific product.
Other medicine groups
Statins
Statins lower LDL cholesterol by slowing the liver's own cholesterol production, and are prescribed to reduce the long-term risk of heart attack and stroke.
Metformin
Metformin lowers blood glucose mainly by reducing the amount of glucose the liver releases, and is usually the first medicine used in type 2 diabetes.
Levothyroxine
Levothyroxine replaces the thyroid hormone the body is not making enough of, in an underactive thyroid.
Warfarin
Warfarin thins the blood by blocking the vitamin K-dependent clotting factors, and is used to prevent and treat blood clots.
DOACs (direct oral anticoagulants)
DOACs thin the blood by directly blocking a single clotting factor, and are used to prevent stroke in atrial fibrillation and to treat and prevent venous clots.
SSRIs and SNRIs
These antidepressants raise the availability of serotonin (and for SNRIs also noradrenaline) in the brain, and are used for depression and several anxiety conditions.
All medicine groups · Alcohol units and clearance · Blood test reference ranges
Track meals and symptoms alongside your medicines
TempoLife keeps your food, symptoms and the medicines you take in one place, so a pattern is easy to show your pharmacist or doctor.