The search for a cure for the common cold has produced a long list of medicines and supplements. Zinc is among the most studied, yet it is not a cure and the evidence does not support every product or claim.
Interest in zinc has risen and fallen as studies have produced different results. The research is difficult to compare because trials have used different zinc salts, doses, lozenge ingredients, schedules and definitions of recovery. Evidence about vitamin C and echinacea is also mixed or limited and should not be interpreted as proof that supplements prevent or cure colds.
What research suggests
Reviews of clinical trials have suggested that certain oral zinc lozenges may reduce the length of a cold when treatment begins soon after symptoms start. The average benefit, where observed, has generally been modest. Not every trial has found an effect, and uncertainty remains about the best formulation, dose and treatment schedule.
There is much less support for taking zinc routinely to prevent colds. Results from short treatment trials cannot establish that long-term supplementation is useful or safe.
Why formulations matter
Zinc acetate and zinc gluconate have commonly been used in lozenge studies. However, a label naming one of these forms does not guarantee that a product will match a successful trial. The amount of elemental zinc, other ingredients and how the lozenge dissolves may influence how much zinc is available in the mouth and throat.
Researchers have proposed several mechanisms, including interference with viral attachment or replication and effects on inflammation. These laboratory explanations are plausible but do not establish that a particular retail product will deliver a meaningful clinical benefit.
Avoid zinc products used in the nose
Intranasal zinc products have been associated with loss of smell, which can be long-lasting. Do not put zinc gels, sprays or swabs into the nose. Seek medical advice if your sense of smell changes.
Side effects and interactions
Short-term oral zinc use can cause nausea, vomiting, stomach cramps, diarrhea, mouth irritation and a metallic or unpleasant taste. Taking high doses for prolonged periods can reduce copper absorption and may contribute to copper deficiency, anemia, neurological problems and altered immune function.
Zinc can interact with some medicines, including certain antibiotics and penicillamine. Timing doses apart may be necessary, but the appropriate interval depends on the medicine. A pharmacist or clinician can review the product, dose and medication schedule.
Zinc in the diet
Zinc is an essential mineral involved in immune function, cell division, wound healing and the senses of taste and smell. It is found in foods including oysters and other seafood, meat, poultry, dairy foods, beans, nuts and fortified cereals. Plant compounds called phytates can reduce absorption from some foods, though varied eating patterns can still provide zinc.
More is not necessarily better. A supplement used briefly for cold symptoms may provide much more than the amount needed each day. People who already use a multivitamin or another zinc-containing product should total the zinc from all sources before adding a lozenge.
Practical bottom line
If you are considering an oral zinc lozenge, ask a pharmacist whether the formulation and dose are suitable for you. Starting soon after symptoms appear may matter, but benefit is uncertain. Follow the label, do not exceed its directions and do not continue high-dose zinc as a long-term prevention strategy.
Children, people who are pregnant or breastfeeding, and anyone taking prescription medicine should get individual guidance before using a zinc cold product. Contact a health professional for severe symptoms, breathing difficulty, dehydration, a persistent or worsening illness, or concerns about a higher-risk medical condition.