Does zinc help a cold?

What does the research actually say about zinc and colds?

The results depend on which review you read, which is why you see such different claims online.

A 2024 Cochrane review pooled 34 randomized trials with about 8,500 people. In treatment trials, zinc may have shortened colds by about 2 days on average. But the authors rated this low certainty, the trial results varied a lot, and they cautioned that the studies differed widely in how zinc was given and what they measured.

The National Center for Complementary and Integrative Health (NCCIH) lists oral zinc among cold remedies that have shown some promise. It says lozenges may shorten a cold when started within 24 hours of symptoms and taken for less than 2 weeks. The NIH Office of Dietary Supplements says zinc lozenges or syrup may speed recovery if started at the start of a cold, but don't seem to make symptoms less severe.

• Shortening a cold: possible, if started early. Low certainty.
• Making symptoms milder: no clear effect.
• Preventing colds: the 2024 Cochrane review found zinc may make little or no difference (low certainty).
• Best dose and form: not settled. The NIH says more study is needed.

When should you start zinc lozenges, and for how long?

Timing matters. The studies NCCIH describes started zinc within 24 hours of the first symptoms. If you are already several days in, it's much less clear that zinc will help.

Keep it short. NCCIH describes use for less than 2 weeks. Taking high doses of zinc for a long time can cause other problems (see below).

Follow the dosing on the product label. In many cold trials, the daily totals were above the 40 mg adult upper limit listed by the NIH. The NIH says its upper limits don't apply to people taking zinc for medical reasons under a doctor's care. If you want to go above the label, check with a clinician or pharmacist first.

What side effects does zinc cause?

The 2024 Cochrane review found that people taking zinc for a cold probably had more non-serious side effects than people taking a placebo. NCCIH lists bad taste and nausea as the ones people report.

• Bad or metallic taste in the mouth
• Nausea or upset stomach
• Too much zinc: the NIH lists nausea, dizziness, headaches, vomiting, and loss of appetite as signs.
• Long-term high doses: can lower copper levels, weaken immunity, and lower HDL (good) cholesterol, according to the NIH.

Are zinc nasal sprays safe?

No. Skip any zinc product you put in your nose, such as gels, swabs, or sprays.

NCCIH says intranasal zinc can cause loss of the sense of smell, which may be long-lasting or permanent. In 2009, the FDA told consumers to stop using several intranasal zinc cold products for this reason. NCCIH's conclusion is that the risk of a serious, lasting side effect outweighs any possible benefit.

Some over-the-counter cold products labeled as homeopathic contain zinc, so read the label. If you used a zinc nasal product and your sense of smell changed, tell a clinician.

Who should check before taking zinc?

Zinc can interact with some common medicines. The NIH Office of Dietary Supplements gives these examples:

• Quinolone antibiotics (like Cipro) and tetracycline antibiotics: zinc can reduce how much of both you absorb. Take the antibiotic at least 2 hours before, or 4 to 6 hours after, zinc.
• Penicillamine (for rheumatoid arthritis or Wilson disease): take it at least 1 hour apart from zinc.
• Thiazide diuretics (like hydrochlorothiazide): these increase zinc loss in urine over time.
• Kids: the NIH upper limits are much lower for children, for example 7 mg a day for ages 1 to 3 and 12 mg for ages 4 to 8. CDC says not to give lozenges to children under 4. Ask your child's doctor before using zinc for a cold.