Supplement Safety Guide
Supplements can be genuinely useful — but they are not regulated like prescription drugs. That means quality varies wildly, some products contain ingredients not listed on the label, and certain combinations can interact with medication. Here is how to protect yourself.
Drug Interactions to Watch
- St John’s Wort — reduces the effectiveness of the contraceptive pill, antidepressants, blood thinners, and HIV medications.
- Vitamin K — can counteract warfarin and other anticoagulants.
- Calcium — can reduce absorption of thyroid medication and certain antibiotics. Take them at least 2 hours apart.
- Fish oil / Omega-3 — may increase bleeding risk if combined with blood thinners.
- Iron — interferes with absorption of levothyroxine and some antibiotics.
If you take any prescription medication, check with your GP or pharmacist before adding a new supplement.
Quality Certifications
Look for products that carry at least one third-party certification:
- GMP (Good Manufacturing Practice) — the facility follows standardised production and quality control processes.
- NSF International — independent testing confirms the product contains what the label says and nothing else.
- Informed Sport — batch-tested for banned substances. Essential for competitive athletes.
- USP Verified — the US Pharmacopeia has verified purity, potency, and manufacturing standards.
How to Read a Supplement Label
- Check the serving size — some products list nutrients per two or three capsules, not one.
- Look at the active ingredient form — magnesium glycinate absorbs better than magnesium oxide, for example.
- Check for fillers and additives — titanium dioxide, artificial colours, and unnecessary binders.
- Verify the % NRV (Nutrient Reference Value) — anything over 1,000 % without medical advice is a red flag.
Red Flags
- Claims that sound too good to be true (“cures cancer”, “lose 10 lbs in a week”).
- Proprietary blends that hide individual ingredient doses.
- No third-party testing or certification logos.
- Sold only through social media with no proper business address.
- Mega-doses far above the tolerable upper intake level.
When to Consult a Doctor
- You are pregnant, breastfeeding, or trying to conceive.
- You take prescription medication of any kind.
- You have a chronic condition (kidney disease, liver disease, diabetes).
- You are under 18 or over 65.
- You experience side effects after starting a new supplement.
Disclaimer: The information on this page is for educational purposes only and is not a substitute for professional medical advice. Always consult a qualified healthcare provider before starting any supplement regimen.
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