Your questions answered

Most coughs, colds, sore throats and ear infections are caused by viruses, and antibiotics do nothing for viruses. Your clinician weighs up how likely a bacterial infection is against the harm antibiotics can cause. If you are not improving in the timeframe you were given, go back.

It is a prescription you only collect or use if you are not getting better after a few days, or if you get worse. It avoids taking antibiotics you may never need.

Most courses in UK general practice are 3 to 7 days, and each infection page on this site shows the usual length. Some people need much longer or preventive courses — for example after certain cancers, chemotherapy or transplants — and should follow their specialist's plan.

No. Never take leftover or shared antibiotics unless a healthcare professional has expressly told you to. The wrong antibiotic can delay treatment, cause side effects and drive resistance. Return leftovers to a pharmacy.

Feeling sick, mild diarrhoea, stomach discomfort and thrush are common with many antibiotics. They usually settle during or shortly after the course. Each antibiotic page lists what to expect for that specific medicine.

Stop the medicine and call 999 or go to A&E for swelling of the face, lips or throat, difficulty breathing, or a blistering or peeling rash, or sores in the mouth or eyes. Contact your doctor or NHS 111 the same day for severe watery or bloody diarrhoea, or yellowing of the skin or eyes.

Do not stop on your own for mild effects — speak to your pharmacist or doctor first, as they may be able to help you manage them or switch you. Stop and seek help immediately for the warning signs above.

Do not drink alcohol while taking metronidazole or tinidazole, as it can cause severe flushing, vomiting and a racing heart. Avoid it for 48 hours after finishing metronidazole and 72 hours after finishing tinidazole. With most other antibiotics a small amount is unlikely to interact, but alcohol will not help you recover.

Most antibiotics do not reduce how well the pill works. Rifampicin and rifabutin do. If you are vomiting or have severe diarrhoea, absorption can be affected — use extra precautions and ask your pharmacist.

There is no strong evidence that you need them. Eating and drinking normally, and staying hydrated if you have diarrhoea, matters more.

No. Nausea, diarrhoea and headache are side effects, not allergy. A true allergy involves hives, swelling, wheeze or a widespread rash. Immediate reactions often start within an hour, but delayed allergic reactions can appear hours or days later. Ask a clinician to assess any rash, and do not remove an allergy label yourself. Read the full explainer.

Often not. Around 9 in 10 people labelled penicillin allergic are not allergic when tested. Being wrongly labelled means you get second-choice antibiotics that may work less well. Ask your doctor about being reassessed or referred for allergy testing.

Penicillins such as amoxicillin, phenoxymethylpenicillin, flucloxacillin and co-amoxiclav. Cephalosporins are used with caution depending on the reaction. Common alternatives include macrolides such as clarithromycin, or tetracyclines such as doxycycline. Your prescriber will choose the right one for your infection.

Take it as soon as you remember, unless your next dose is nearly due. Never take a double dose to catch up. If you miss several, ask your pharmacist.

Take it exactly as prescribed, for the length you were given. If you feel you should stop early because of side effects, speak to your prescriber or pharmacist rather than deciding alone.

Many people improve within 48 to 72 hours. If you are no better by then, or you feel worse at any point, contact your doctor or NHS 111 the same day.

Use the consultation notes to record what you were prescribed and for how long, and the symptom diary to log how you feel each day.