Activated charcoal

What it is

Activated charcoal is a porous form of carbon with a very large surface area. It is not absorbed from the gut; instead it binds gases and some substances inside the intestine and carries them out in the stool. It is used over the counter for short-lived bloating and for simple diarrhoea.

A usual adult range, not a national label — the dose and the timing differ by country and by product.

Used for

• Bloating
• Diarrhoea

Approved uses differ by country — some of these may be off-label or unapproved where you live.

What to know while taking it

It is taken between meals rather than with food, since food in the stomach competes for the same binding surface. The binding is indiscriminate, so other medicines taken close to it — including contraceptives and prescription tablets — can be partly bound and lose effect; a gap of about two hours on either side is the usual precaution. It is meant for short courses only: prolonged use can interfere with the absorption of nutrients and mask a problem that needs looking into. The stool turns black while it is being taken, which is expected and not bleeding.

When to see a doctor

Diarrhoea that continues beyond a few days, fever, blood in the stool, severe or persistent abdominal pain, or signs of dehydration mean it is time to stop guessing and see a doctor. Constipation or an inability to pass stool while taking it also warrants medical advice.

Worth knowing

• Separate from other medicines by 2 hours
• Short courses only