Zinc, honestly — the cold remedy with real caveats

Zinc is a genuinely essential mineral with a modest, much-hyped role in colds. The honest headline: zinc lozenges may shorten a cold a little, but the evidence is uncertain and comes with real caveats on dose, taste and side effects — and nasal zinc should be avoided.

Essential mineral, modest cold role

Zinc is required for immunity, wound healing and hundreds of enzymes, and a real deficiency impairs immune function. The popular use, though, is taking zinc lozenges to shorten a cold — a claim with some support and plenty of caveats.

What the evidence shows

A possible small effect, low certainty.

• Lozenges may shorten a cold — Pooled trials suggest zinc may reduce cold duration (on the order of a couple of days), but the evidence is low-certainty and results vary a lot with dose, form and how quickly it’s started. (emerging)
• Real side effects and limits — Zinc lozenges commonly cause bad taste and nausea, and high ongoing intake can cause copper deficiency. It’s not a benign "more is better" supplement. (note)
• Avoid intranasal zinc — Zinc nasal sprays and gels have been linked to loss of smell, sometimes lasting. Skip nasal zinc products. (note)

What we still don’t know

• The right form, dose and timing Which zinc formulation and dose (if any) reliably helps, and how early it must start, remain uncertain across trials.
• How big the real effect is Because the evidence is low-certainty and heterogeneous, the true size of any benefit is unclear.

Key terms

• Zinc An essential mineral for immunity and enzymes; modestly and uncertainly linked to shorter colds when taken as lozenges.
• Lozenge A tablet dissolved slowly in the mouth — the zinc form with the most (still uncertain) cold evidence.
• Anosmia Loss of the sense of smell — a risk linked to intranasal zinc products.
• Copper deficiency A shortfall of copper that high, prolonged zinc intake can cause.