This article is for general information only and is not medical advice. It cannot tell you whether your symptoms are serious. If you are worried, speak to a health professional.
First: when to get help now
Call 999 or go to A&E if:
- you have sudden chest pain or discomfort that doesn’t go away
- the pain spreads to your arms, back, neck, jaw or stomach
- your chest feels tight or heavy, or you are struggling to breathe or get words out
- you feel sweaty, sick, light-headed or suddenly confused
- your lips or skin are turning pale, blue or grey
- you have swelling of the lips, face or throat, or a sudden rash with wheezing, after taking anything new
Call NHS 111 if you are more short of breath than usual, or breathless with palpitations. See the NHS pages on chest pain and shortness of breath for the full advice.
Don’t wait to see whether stopping a supplement helps. Get checked first.
The short answer
A tight chest or trouble breathing is not a normal side effect of magnesium at ordinary doses. It can happen for reasons that have nothing to do with the supplement, and a few that do. Because some of the causes are serious, the right response is always the same: stop taking the magnesium and get medical advice. Don’t try to fix it by adjusting other supplements.
Possible links with magnesium
Very high magnesium levels
Too much magnesium in the blood relaxes muscles, including the ones used for breathing. The NIH lists difficulty breathing among the signs of magnesium toxicity, along with low blood pressure, nausea, flushing, lethargy, muscle weakness and an irregular heartbeat.
This is rare. Healthy kidneys remove extra magnesium, so it mostly happens in people with kidney disease or in those taking very large doses, usually from magnesium-based laxatives or antacids. It is a medical emergency.
A reaction to the product
Any supplement can cause an allergic reaction, to the capsule, a filler, a flavouring or another active ingredient. Wheezing, chest tightness, a rash or swelling shortly after a dose should be treated as an emergency.
Reflux and indigestion
Tablets and capsules can irritate the gullet or stomach, especially taken without food or water or just before lying down. Heartburn can feel like chest tightness. It still needs checking the first time it happens, because it is hard to tell apart from heart pain.
Palpitations and anxiety
Being aware of your heartbeat, or feeling anxious about a new supplement, can make the chest feel tight and breathing feel short. Panic attacks are one of the common causes of breathlessness listed by the NHS. This is a diagnosis for a clinician to make once other causes have been ruled out, not one to assume.
Causes that have nothing to do with magnesium
Asthma, chest infections, heart problems, blood clots and anaemia can all start at any time, including the week you happened to open a new bottle of supplements. This is the main reason not to self-diagnose.
What to do next
- Stop taking the magnesium. It is safe to stop suddenly.
- Get medical advice, urgently if any of the signs at the top of this page apply.
- Take the product with you or note its name, dose and ingredients, along with anything else you take.
- Don’t restart until a doctor or pharmacist has said it is fine to.
An earlier version of this article suggested taking calcium and vitamin D to counter breathing problems caused by magnesium. We have removed that advice. It isn’t supported by evidence, and it could delay someone getting urgent care.
Who should check with a doctor before taking magnesium
- anyone with kidney disease or reduced kidney function
- anyone with a heart condition or taking heart or blood pressure medicine
- anyone with a lung condition such as asthma or COPD who notices a change in their breathing
- anyone who is pregnant, breastfeeding or taking regular prescribed medicine
The NHS says 400 mg or less a day of magnesium from supplements is unlikely to cause harm in adults. Remember to count indigestion and constipation remedies, which can contain far more.
Related reading
Once you have been checked and want to understand how magnesium relates to other nutrients, our free Mineral Interaction Wheel shows what it works with and what it may compete with. Our magnesium side effects guide covers the milder, more common side effects.
Sources
- NHS. Chest pain.
- NHS. Shortness of breath.
- NIH Office of Dietary Supplements. Magnesium: Fact Sheet for Health Professionals.
- NHS. Vitamins and minerals: Others (magnesium).