Mefenamic Acid 500mg Tablets

Mefenamic acid is a prescription anti-inflammatory painkiller (an NSAID). It's mainly used to relieve period pain and to make heavy periods lighter. The usual adult dose is one 500mg tablet three times a day, taken with or after food. At MedsRus, a UK prescriber reviews a short online consultation before supplying mefenamic acid, and we send it in discreet packaging.

Mefenamic acid at a glance

What is mefenamic acid used for?

Mefenamic acid is used for:

• period pain (dysmenorrhoea), including cramps in the tummy, back and thighs;
• heavy periods (menorrhagia), where it can reduce how much you bleed;
• other mild to moderate pain, such as muscle and joint pain, although other anti-inflammatories are more often used for these.

For a wider look at period pain and the alternatives, see our page on period pain relief.

How does mefenamic acid work?

During your period, the lining of the womb releases chemicals called prostaglandins. They make the womb muscles contract, which causes cramping pain, and they also play a part in how heavily you bleed.

Mefenamic acid blocks the enzymes your body uses to make prostaglandins. With fewer prostaglandins, the womb contracts less, so you get less pain, and bleeding is often lighter too. This is why it works better for period pain than paracetamol, which doesn't reduce prostaglandins.

Mefenamic acid dosage

How many times a day should I take mefenamic acid?

The usual dose for adults is 500mg three times a day, for example with breakfast, lunch and dinner. Don't take more than 1,500mg in 24 hours.

• For period pain: start when the pain starts, or when your period starts if pain usually comes with it.
• For heavy periods: start on the first day of bleeding.
• Take it regularly for as long as you need it during your period, usually 3 to 5 days.
• If you're older or have kidney problems, the prescriber may suggest a lower dose.

How to take it

• Swallow the tablet whole with a glass of water. Don't chew or crush it.
• Take it with or just after food to protect your stomach.
• If you miss a dose, take it as soon as you remember, unless it's nearly time for the next one. Never take two doses together.
• If you take too much, get medical help straight away, even if you feel well. An overdose can cause fits (seizures).

Side effects of mefenamic acid

Most people take mefenamic acid without problems, especially in short courses.

Common side effects include:

• diarrhoea;
• feeling sick or being sick;
• indigestion or tummy pain;
• headache;
• feeling dizzy or drowsy.

Stop taking it and speak to a doctor or pharmacist if you get diarrhoea or a skin rash. Diarrhoea is a known side effect of mefenamic acid that means you should stop.

Serious side effects

These are rare. Get urgent medical help if you:

• have black, tarry or bloody poo, or vomit blood or something that looks like coffee grounds;
• have severe tummy pain;
• get wheezing or shortness of breath;
• have swelling of your face, lips, tongue or throat, or a severe skin reaction such as blistering;
• notice yellow skin or eyes, or unusual bruising or bleeding.

Don't drive or use machinery if mefenamic acid makes you dizzy or drowsy.

Who shouldn't take mefenamic acid?

It may not be suitable if you:

• have, or have had, a stomach ulcer or bleeding;
• have inflammatory bowel disease, such as Crohn's disease or ulcerative colitis;
• have asthma that gets worse with ibuprofen, aspirin or other NSAIDs;
• have severe heart, liver or kidney problems;
• are pregnant, trying to get pregnant or breastfeeding, unless a doctor has said it's safe. Don't take it at all from 20 weeks of pregnancy.

Medicines to check

Tell the prescriber if you take:

• other anti-inflammatory painkillers, such as ibuprofen, naproxen or aspirin. Don't take these with mefenamic acid;
• blood thinners such as warfarin;
• some antidepressants (SSRIs);
• lithium or methotrexate;
• medicines for high blood pressure or water tablets.

You can take paracetamol with mefenamic acid if you need extra pain relief.

Mefenamic acid vs other period pain treatments

• Ibuprofen is an anti-inflammatory you can buy without a prescription. It works in a similar way and is often tried first.
• Naproxen is a longer-acting anti-inflammatory, taken twice a day.
• Mefenamic acid also reduces heavy bleeding, so it suits people who have painful and heavy periods.
• Hormonal contraception, such as the combined pill, can make periods lighter and less painful. See our contraceptive pill page.

See a GP if your periods are very heavy, your pain is getting worse over time, or you have pain during sex or bleeding between periods. These can be signs of conditions such as endometriosis or fibroids.

How to order mefenamic acid from MedsRus

1. Complete a short consultation about your periods, your health and any medicines you take.
2. A UK prescriber reviews it and, if mefenamic acid is suitable, approves your order.
3. We send it in discreet packaging.

Mefenamic acid FAQs

What is mefenamic acid used for?

Mainly for period pain and heavy periods. It can also be used for other mild to moderate pain.

How many times a day can I take mefenamic acid 500mg?

Usually three times a day, with food. Don't take more than 1,500mg in 24 hours.

How long does mefenamic acid take to work?

It usually starts to ease pain within about an hour.

Can I take mefenamic acid with ibuprofen?

No. They're both anti-inflammatories, and taking them together raises the risk of side effects. You can take paracetamol with it.

Does mefenamic acid stop periods?

No, but it can make heavy periods lighter while you take it.

Can I drink alcohol with mefenamic acid?

A small amount is usually fine, but alcohol increases the risk of stomach irritation.

Can I take mefenamic acid with paracetamol?

Yes. Paracetamol works in a different way, so you can take it alongside mefenamic acid if you need extra pain relief. Don't take other anti-inflammatory painkillers, such as ibuprofen or naproxen, with it, and tell the prescriber if you take low-dose aspirin.

Mefenamic acid or tranexamic acid for heavy periods?

Tranexamic acid reduces heavy bleeding but doesn't help with pain. Mefenamic acid can help with both period pain and heavy bleeding. A prescriber can advise which suits you.

Further reading

• Period pain relief
• Pain relief tablets

Sources:

• BNF: Mefenamic acid
• NHS: NSAIDs
• NHS: Heavy periods