Supplements can cause side effects, interact with prescription medicines, and cause harm at high doses. Being sold without a prescription and marketed as natural does not change that; it changes how closely the product is checked before it reaches you.
Most people take supplements without difficulty. The problems that do occur cluster into a few recognisable situations rather than being spread evenly across every product.
Common side effects reported with this supplement or ingredient
By category, the effects reported most often:
- Minerals. Digestive effects dominate: diarrhoea from magnesium, constipation from iron, nausea from zinc on an empty stomach.
- Fat-soluble vitamins. Vitamins A, D, E and K accumulate rather than being excreted, so sustained excess is the concern. See vitamin D.
- Herbal products. Mainly an interaction problem rather than a side-effect one. See herbal supplement side effects.
- Stimulant-based products. Fat burners and pre-workouts cause palpitations, anxiety and insomnia. See pre-workout side effects.
- Protein and gut products. Bloating, wind and looser stools, usually settling.
Possible interactions with medicines, chronic conditions or pregnancy
This is where supplements cause the most serious harm, and where they are most often overlooked, because people do not think of them as medicines when asked what they take.
- St John’s Wort, which reduces the effectiveness of contraception, warfarin, HIV medicines and more. See St John’s Wort interactions.
- Anything affecting bleeding alongside blood thinners: fish oil, turmeric, ginkgo, garlic, vitamin E. See supplements and blood thinners.
- Minerals blocking absorption of thyroid medicine and some antibiotics.
- Blood sugar and blood pressure products adding to prescribed treatment. See supplements with diabetes medication.
See supplement and medicine interactions for the full picture.
Who should speak to a healthcare professional before using it?
- Anyone taking prescription medicine, particularly blood thinners, epilepsy medicines, HIV medicines, transplant medicines or contraception
- Anyone pregnant or breastfeeding
- Anyone with kidney or liver disease
- Anyone with surgery planned
- Anyone taking a supplement to treat a symptom rather than for general cover, since a symptom deserves a diagnosis
Dose, product-quality and stacking risks
Supplements in South Africa are regulated as complementary medicines, and the checks applied are not the same as those for prescription medicines. Strength, purity and labelling can vary between products. See how supplements are regulated in South Africa and how to check supplement labels.
Stacking is the most common way people take too much. A multivitamin, a standalone vitamin, a fortified drink and a category formula can deliver several times the intended amount of overlapping ingredients. Lay out everything you take and read the ingredient panels together. See taking too many supplements.
Sports and weight-loss products carry an additional risk: undeclared ingredients, including stimulants and in some cases anabolic substances not listed on the label. See unsafe supplements in South Africa.
When to stop and get medical advice
Get urgent help for difficulty breathing or facial swelling, chest pain or a racing heartbeat, unusual bruising or bleeding, or severe abdominal pain.
Stop and seek advice for yellowing of the eyes or skin, dark urine, persistent nausea or unexplained tiredness, which can indicate liver problems. See supplements causing liver problems and when to see a doctor about a supplement.
Unlike prescription medicines, supplements can generally be stopped without a tapering plan. If you suspect one is causing a problem, stopping it and asking is a reasonable first step. Do not stop a prescribed medicine on the same reasoning.
Related supplement safety guides
- Supplement and medicine interactions
- Taking too many supplements
- When to see a doctor about a supplement
- Unsafe supplements in South Africa
- Report a supplement side effect in South Africa
Medical Disclaimer: This content is for informational and educational purposes only and does not constitute medical diagnosis, prescription, or professional advice. Always read the patient information leaflet and consult a qualified doctor or pharmacist regarding any medicine or health concern.