1. About cefalexin

Cefalexin is an antibiotic. It belongs to a group of antibiotics called cephalosporins.

It's used to treat bacterial infections, such as pneumonia and other chest infections, skin infections and urinary tract infections (UTIs).

Cefalexin is only available on prescription. It comes as capsules, tablets or as a liquid for children and people who find it difficult to swallow capsules or tablets.

2. Key facts

  • You'll usually start to feel better in a few days, depending on the type of infection you have.
  • The most common side effects of cefalexin are feeling sick (nausea) and diarrhoea.
  • You can drink alcohol while taking cefalexin.
  • It's important to keep taking cefalexin until you've completed the course, even if you feel better.

3. Who can and cannot take cefalexin

Cefalexin can be taken by most adults and children.

Cefalexin is not suitable for some people. To make sure cefalexin is safe for you, tell your doctor if you have:

  • had an allergic reaction to cefalexin or any other medicine in the past
  • kidney problems
  • ever had a severe skin rash or skin peeling, blistering and/or mouth sores after taking antibiotics
  • had severe or bloody diarrhoea when you've taken antibiotics before

4. How and when to take it

Always follow the advice of your doctor and the instructions that come with your medicine.


The dose of cefalexin can vary but for most infections you will take 500mg, two or three times a day.

The dose may be higher for severe infections and lower for children.

Try to space the doses evenly throughout the day. If you take it 3 times a day, this could be first thing in the morning, mid-afternoon and at bedtime.


Keep taking this medicine until you've completed the course, even if you feel better. If you stop your treatment early, the infection could come back.

How to take it

Cefalexin can be taken with or without food.

Capsules or tablets – swallow whole with a drink of water. Do not chew or break them.

Liquid – if you or your child are taking cefalexin as a liquid, it will usually be made up for you by a pharmacist. The medicine will come with a plastic syringe or medicine spoon to help you measure the right dose. If you do not have one, ask a pharmacist for one. Do not use a kitchen teaspoon as it will not give the right amount.

What if I forget to take it?

If you forget to take a dose, take it as soon as you remember, unless it's nearly time for your next dose. In this case, skip the missed dose and take your next dose at the usual time. Try to leave a gap of at least 4 hours between doses.

Never take 2 doses at the same time. Never take an extra dose to make up for a forgotten one.

If you forget doses often, it may help to set an alarm to remind you. You could also ask a pharmacist for advice on other ways to remember your medicines.

What if I take too much?

Accidentally taking 1 extra dose of cefalexin is unlikely to harm you or your child.

Speak to a pharmacist or doctor if you're worried or you take 2 extra doses or more.

5. Side effects

Like all medicines, cefalexin can cause side effects, although not everyone gets them.

Fewer than 1 in 100 people may have an allergic reaction to cefalexin. In most cases, the allergic reaction is mild.

Common side effects

These common side effects happen in around 1 in 10 people.

Keep taking the medicine, but talk to your doctor or pharmacist if these side effects bother you or do not go away:

  • feeling sick (nausea)
  • diarrhoea
  • stomach pain

Serious side effects

Serious side effects are rare and happen in less than 1 in 1,000 people.

Call your doctor immediately if you get:

  • severe diarrhoea that lasts for more than 4 days or contains blood or mucus
  • pale poo and dark pee, yellowing of your skin or whites of your eyes – this may be a sign of liver problems
  • bruised skin

Serious allergic reaction

In rare cases, cefalexin can cause a serious allergic reaction (anaphylaxis).

These are not all the side effects of cefalexin. For a full list see the leaflet inside your medicine packet.


You can report any suspected side effect to the UK safety scheme.

6. How to cope with side effects

What to do about:

  • feeling sick – eat simple meals and do not eat rich or spicy food while you're taking this medicine. It might help to take your cefalexin after a meal or snack.
  • diarrhoea – drink lots of fluids, such as water or squash, to avoid dehydration. Signs of dehydration include peeing less than usual or having dark, strong-smelling pee. Do not take any other medicines to treat diarrhoea without speaking to a pharmacist or doctor.
  • stomach pain – putting a heat pad or covered hot water bottle on your stomach may help stomach pain.

7. Pregnancy and breastfeeding

It's usually safe to take cefalexin during pregnancy and while breastfeeding.

Read about how cephalosporin antibiotics like cefalexin can affect you and your baby on the Best Use of Medicines in Pregnancy (BUMPS) website.


For safety, tell your doctor if you're trying to get pregnant, are already pregnant or if you're breastfeeding.

8. Cautions with other medicines

There are some medicines that do not mix well with cefalexin.

Tell your doctor if you're taking any of these medicines before you start taking cefalexin:

  • probenecid (a medicine used to treat gout)
  • metformin (a medicine used to treat diabetes)
  • medicines that make you pee more (diuretics) including furosemide
  • other antibiotics

Mixing cefalexin with herbal remedies and supplements

Do not take cefalexin at the same time as zinc supplements or anything with zinc in it. This is important because zinc may reduce the amount of cefalexin in your body, meaning the medicine cannot work as it's meant to.

If you do take supplements with zinc in them, make sure there is a gap of at least 3 hours before and after you take your cefalexin.


For safety, tell your doctor or a pharmacist if you're taking any other medicines, including herbal remedies, vitamins or supplements.

9. Common questions

Page last reviewed: 20/03/2020
Next review due: 20/03/2023