Who Should Not Take Zinc Supplements
Zinc is one of the most popular minerals among people who train, usually taken for immunity, testosterone support or recovery. It is generally well tolerated, yet there are clear situations in which a zinc supplement is unnecessary, inappropriate or even harmful. The editorial team sets out who should avoid it or take it only under medical supervision.
Why zinc is not automatically harmless
Zinc is an essential trace element involved in hundreds of enzymes, in immune function, wound healing, protein synthesis and the production of hormones, including testosterone. A genuine deficiency impairs all of these processes, which is why zinc has earned a reputation as a "must-have" for athletes.
The flip side is that the body has no dedicated mechanism for storing large amounts of zinc. Excess intake competes with other minerals for absorption, most notably copper and, to a lesser extent, iron. Long-term overuse can therefore create a new deficiency while trying to prevent another.
In the UK, the reference nutrient intake (RNI) is 9.5 mg per day for adult men and 7 mg for adult women. The Expert Group on Vitamins and Minerals set a safe upper level of 25 mg per day of supplemental zinc for lifelong use, and the European Food Safety Authority has set a tolerable upper intake level of 25 mg per day from all sources.
Many sports products contain 15–30 mg in one capsule, and some "ZMA" formulas provide similar amounts alongside magnesium. Add a multivitamin and a zinc-fortified cereal, and it becomes easy to exceed the upper level without realising it. That makes the question of who should not take zinc a practical one, not just a theoretical one.
People with low copper or at risk of copper deficiency
The most important contraindication to long-term zinc supplementation is existing or potential copper deficiency. Zinc stimulates the production of metallothionein in intestinal cells, a protein that binds copper more tightly than zinc and traps it so it is lost when the cells are shed.
Zinc-induced copper deficiency is well documented. It can cause anaemia that does not respond to iron, a low white blood cell count (neutropenia) and, in more severe or prolonged cases, nerve damage affecting the spinal cord, with numbness, gait problems and weakness. Neurological damage may be only partly reversible.
People at higher risk include those who have had bariatric surgery, those with malabsorption conditions such as coeliac disease or inflammatory bowel disease, and anyone already taking high doses of zinc for months. Denture creams containing zinc have also been implicated in case reports when used in very large amounts.
For these groups, zinc should only be taken after a discussion with a GP, ideally with blood tests for copper and caeruloplasmin, and usually with a deliberate plan to monitor both minerals.
Medicines that interact with zinc
Zinc can bind to certain drugs in the gut and reduce their absorption, while some medicines alter how much zinc the body retains or loses. The table below summarises the interactions most often highlighted in the British National Formulary and pharmacology references.
| Medicine or group | Nature of the interaction | Practical consequence |
|---|---|---|
| Quinolone antibiotics (e.g. ciprofloxacin) | Zinc binds the antibiotic in the gut | Antibiotic may not work properly; doses must be separated |
| Tetracyclines (e.g. doxycycline) | Chelation and reduced absorption | Separate by several hours, follow pharmacist advice |
| Penicillamine | Mutual reduction in absorption | Only under specialist supervision |
| Thiazide diuretics | Increase urinary zinc loss | Discuss supplementation with the prescriber |
| Oral iron supplements | Compete for absorption at high doses | Take at different times if both are needed |
| Eltrombopag and some other drugs | Polyvalent cations reduce absorption | Check timing with a pharmacist |
The common thread is timing and supervision rather than an absolute ban. Someone prescribed a course of ciprofloxacin, for example, may simply need to pause zinc for the duration or take it at a well-separated time. The decision should come from the pharmacist or prescriber, not from guesswork.
It is also worth remembering that ZMA products, multivitamins and some protein powders contain zinc. When a pharmacist asks about supplements, all of these should be mentioned, not only products labelled as "zinc".
Medical conditions that call for caution
Several health conditions make unsupervised zinc supplementation unwise. In chronic kidney disease, mineral handling is altered and supplement use should always be agreed with the renal team. Interestingly, people on dialysis may in fact be zinc-deficient, which is precisely why the decision needs a specialist.
Wilson's disease is a special case. Zinc acetate is actually used as a treatment because it blocks copper absorption. However, this is a prescribed therapy with careful monitoring, not a reason for self-medication, and dosing is entirely the specialist's responsibility.
- Chronic kidney disease: only with renal team agreement.
- Known copper deficiency or neuropathy of unclear cause: avoid until investigated.
- Bariatric surgery: use only the regime set by the surgical team.
- Pregnancy and breastfeeding: stay within amounts recommended by the midwife or GP; high-dose products are not appropriate.
- Children: adult-strength products are not suitable.
Another specific warning concerns zinc applied inside the nose. Intranasal zinc gels marketed for colds were associated with cases of persistent or permanent loss of smell, which led to regulatory action in the United States. Lozenges for sore throats are a different form, but nasal zinc products are best avoided completely.
Signs that you are taking too much
Acute high doses of zinc, typically well above 50 mg at once, commonly cause nausea, vomiting, abdominal cramps and diarrhoea. Taking zinc on an empty stomach makes these effects more likely, which is why many people tolerate it better with food despite a small reduction in absorption.
Chronic overuse is more insidious. The early signs of copper depletion are often non-specific: fatigue, frequent infections or abnormal blood counts discovered incidentally. Long-term intakes in the region of 50 mg per day and above have also been associated with lower HDL ("good") cholesterol in some studies.
If you have been taking zinc for several months at doses above the upper level and develop tingling in the hands or feet, balance problems or unexplained anaemia, tell your GP specifically about the zinc. These symptoms can be mistaken for other conditions if the supplement history is not mentioned.
For most healthy adults who eat meat, dairy, legumes and wholegrains, routine zinc supplementation is not necessary. A blood test is not a perfect measure of zinc status, but combined with a dietary review it helps decide whether supplementing makes sense at all.
Conclusions of the editorial team
Zinc is essential, but more is not better. People with copper deficiency or malabsorption, those after bariatric surgery, and anyone with kidney disease should take zinc only under medical supervision.
Zinc interacts with several antibiotics, penicillamine and iron, so timing and pharmacist advice are crucial. Nasal zinc products should be avoided entirely because of the risk of losing the sense of smell.
For most adults, staying within the UK upper level of 25 mg per day of supplemental zinc and counting all sources, including multivitamins and ZMA products, keeps the risks low.
Readers may also find useful our articles on magnesium forms and absorption, on copper as a forgotten mineral for athletes, and on how to interpret a basic blood test panel.
References
- Expert Group on Vitamins and Minerals. Safe Upper Levels for Vitamins and Minerals. London: Food Standards Agency; 2003.
- EFSA Panel on Dietetic Products, Nutrition and Allergies. Scientific opinion on dietary reference values for zinc. EFSA J. 2014;12(10):3844.
- Willis MS, Monaghan SA, Miller ML, et al. Zinc-induced copper deficiency: a report of three cases initially recognized on bone marrow examination. Am J Clin Pathol. 2005;123(1):125–131.
- Prasad AS. Zinc in human health: effect of zinc on immune cells. Mol Med. 2008;14(5–6):353–357.
- Jafek BW, Linschoten MR, Murrow BW. Anosmia after intranasal zinc gluconate use. Am J Rhinol. 2004;18(3):137–141.
- Hemilä H. Zinc lozenges and the common cold: a meta-analysis comparing zinc acetate and zinc gluconate, and the role of zinc dosage. JRSM Open. 2017;8(5):2054270417694291.
