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Magnesium hydroxide

  • Magnesium hydroxide mixture is used for constipation.
  • Take this medicine at bedtime with a glassful of water
  • If you are taking other medicines, do not take magnesium hydroxide within two or three hours (before or after) your other medicines.

About magnesium hydroxide

Type of medicineMagnesium salt
Used forConstipation
Indigestion (in combination products)
Available asMixture

Magnesium hydroxide is used as a laxative to treat constipation. It can also be used in antacid preparations to neutralise excess acid in the stomach.

Constipation is the term used to describe the condition where the stools that are passed are hard and less frequent than normal. It can be caused by a poor diet, not drinking enough water and not going to the toilet as soon as needed. Pregnancy, a lack of exercise or movement (such as being ill in bed) and some medicines, including some pain killers, can also cause constipation. Magnesium hydroxide is an osmotic laxative that works by drawing water into the bowel, which softens stools, making them easier to pass out of the body.

Antacids are taken by mouth to relieve indigestion and heartburn. Acid occurs naturally in the stomach and is produced in response to the presence of food which it helps to break down or digest. Sometimes an excess of acid is produced which irritates the lining of the stomach. Heartburn occurs when acid from the stomach irritates the tube that leads from the mouth into the stomach (the oesophagus). Antacids, such as magnesium hydroxide, neutralise the acid and relieve the discomfort of indigestion and heartburn.

Before taking magnesium hydroxide

Before taking magnesium hydroxide make sure your doctor or pharmacist knows:

  • If you are pregnant, trying for a baby or breast-feeding.
  • If you suffer from kidney or liver problems.
  • If you are suffering from lower tummy pain, cramping, sickness or diarrhoea.
  • If you are taking other medicines, including those available to buy without a prescription, herbal or complementary medicines.
  • If you have ever had an allergic reaction to this or any other medicine.

How to take magnesium hydroxide

  • Before beginning treatment, read the manufacturer's printed information leaflet.
  • Take this medicine exactly as directed by your doctor or pharmacist.
  • Shake the bottle to make sure the medicine is evenly mixed before pouring out a dose.
  • When required for constipation, take the recommended dose with a glass of water at bedtime. The usual dose for an adult is 30-45ml (six to nine 5ml spoonsful), and the dose for a child aged 3 - 12 years is 5-10ml (one or two 5ml spoonsful).

Getting the most from your treatment

  • Do not take this medicine within two to three hours of taking other medicines as it may stop the other medicines working.
  • Magnesium hydroxide is for occasional use only, it should not be taken regularly. Once the constipation eases, you should stop the laxative unless your doctor has told you otherwise.
  • Many people take laxatives when they do not need to because they believe that they should go to the toilet every day. This is not the case as for some people going to the toilet 2-3 times per week is normal.
  • A well balanced diet containing fibre (whole grain breads and cereals, bran, fruit and green leafy vegetables) with 6 to 8 full glasses of water each day and daily exercise are important in maintaining healthy bowel function. For people who have problems with constipation, food such as pastries, puddings, sugar, sweets, cheese and cake can make matters worse.
  • Drinks containing caffeine (tea, coffee, colas) or alcohol can make constipation worse as they have a diuretic effect, which means they cause a loss of fluid from the body, causing dehydration.

Can magnesium hydroxide cause problems?

Along with their useful effects, medicines can cause unwanted side effects. Speak with your doctor or pharmacist if any of the following side effects continue or become troublesome.

Diarrhoea, stomach pain.

If you experience any other symptoms which you think may be due to this medicine, speak with your doctor or pharmacist.

How to store magnesium hydroxide

  • Keep all medicines out of the reach of children.
  • Store in a cool, dry place, away from direct heat and light.

Important information about all medicines


  • If you are having any treatment like an operation or dental treatment, tell the person carrying out the treatment which medicines you are taking.
  • Never take more than the prescribed dose. If you suspect that you or someone else has taken an overdose of this medicine, go to the accident and emergency department of your local hospital at once. Take the container with you, even if it is empty.
  • This medicine is for you. Never give it to other people even if their condition appears to be the same as yours.
  • Never keep out of date or unwanted medicines. Take them to your local pharmacy which will dispose of them for you.
  • If you have any questions about this medicine ask your pharmacist.

References

  • British National Formulary; 55th Edition (March 2008) British Medical Association and Royal Pharmaceutical Society of Great Britain, London (link to current BNF).
Comprehensive patient resources are available at www.patient.co.uk
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dils3830		Last Reviewed:
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