Can I take Fibre supplements and Metformin together?

Why this happens

Fibre supplements (like psyllium husk or glucomannan) work by soaking up water and forming a gel in your gut. This gel can trap the metformin molecules, slowing down or reducing the amount of medicine that passes through your intestinal wall into your bloodstream.

You do not need to stop taking either, but it is best to separate the doses. Try to take your metformin at least 2 hours before or 4 to 6 hours after taking a fibre supplement. Always monitor your blood sugar levels regularly and speak to your doctor if you notice your readings are consistently higher than usual.

Severe kidney or liver problems

You must not take metformin if you have severe kidney or liver failure, as this significantly increases the risk of lactic acidosis, a rare but life-threatening build-up of acid in the blood.

Choking and intestinal blockage

You must take fibre supplements with a full glass of water (at least 200ml). Taking them without enough liquid can cause the supplement to swell and block your throat or oesophagus, leading to choking or bowel obstruction.

Drug absorption interference

Fibre can prevent other medicines from being absorbed properly. Take your other medications at least 1 hour before or 2 to 4 hours after taking a fibre supplement.

Lactic acidosis risk (Dehydration)

If you develop severe vomiting, diarrhoea, or a high fever, stop taking metformin and contact a doctor immediately. These conditions can lead to severe dehydration, which significantly increases the risk of a rare but life-threatening build-up of acid in the blood (lactic acidosis).

Contrast dye scans (e.g., CT or X-ray)

You must tell your doctor you take metformin if you are having a scan involving an injection of 'contrast dye'. You will usually need to stop taking metformin 48 hours before and after the procedure to prevent kidney damage.

Alcohol

It is best to avoid or strictly limit alcohol when taking these supplements. Alcohol can contribute to dehydration, which increases the risk of the supplement causing constipation or a bowel blockage.

It is best to avoid or strictly limit alcohol while taking metformin. Combining alcohol with metformin increases the risk of a rare but serious condition called lactic acidosis (a build-up of lactic acid in the blood). It also increases the risk of low blood sugar (hypoglycaemia).

Water and fluids

You must drink plenty of water (at least 200ml per dose) when taking fibre supplements. If you do not drink enough fluid, the supplement can cause a blockage in your intestine or throat.

Vitamin B12 (Dietary sources)

Long-term use of metformin can lower your vitamin B12 levels. Ensure you eat foods rich in B12 (such as meat, fish, and dairy) or speak to your doctor about monitoring your levels.

Taking multiple medicines? Our Medicines Interaction Checker helps you check whether your prescriptions, over-the-counter medicines, and supplements are safe to take together. Simply search for your medicines to see potential interactions and what to do about them.

Disclaimer

This information is for general educational purposes only and should not be relied upon as a substitute for professional medical advice. Always consult your GP, pharmacist, or another qualified healthcare professional before making decisions about your medications. Individual circumstances may vary, and only a healthcare professional who knows your medical history can provide personalised guidance.