What the Evidence Says About Popular Cold Remedies

Every autumn the same shelf appears in every pharmacy: zinc lozenges, effervescent vitamin C, garlic capsules, little tubes of homeopathic pellets. The honest summary is short. A cold clears up on its own in about a week, sometimes two, and none of these products changes that reliably: the most that has been shown is about two days from zinc, with low certainty. A couple of them have modest support of low certainty, most have almost none, and one form of zinc carries an FDA warning about lasting harm.

When to see a doctor

No supplement belongs in an emergency. Call emergency services — 911 in the United States and Canada, 999 in the United Kingdom, 112 across the EU (in Russia 112, or 103 for an ambulance) — for trouble breathing or shortness of breath, persistent pain or pressure in the chest or abdomen, confusion or being hard to wake, seizures, bluish lips or face, a rash that does not fade when pressed with a glass, or any fever in an infant under 12 weeks. Call a doctor the same day if a fever lasts more than a few days, symptoms drag past ten days without improving, you get better and then clearly worse, or there are signs of dehydration. The full three-tier list for adults and children is on the hub page, what to do at the first signs of a cold.

What is happening

Two things make cold remedies look better than they are. The first is the illness itself: it ends on its own, so whatever you took on the worst day collects the credit for a recovery that was already on its way. The second is timing — people reach for a remedy at the peak of symptoms, and after a peak things improve anyway. That is why "it worked for me" cannot tell a real effect apart from a cold running its course. Only a trial with a control group can, which is what we mean below by evidence. The longer version of this trap is on it got better after treatment.

What to do

Oral zinc. A Cochrane review found that zinc may shorten a cold by around two days, but the certainty of that evidence is low, and non-serious side effects — a bad taste, an upset stomach — are probably more common with it. For preventing colds it shows little or nothing. If you try it, read the package and ask a pharmacist rather than copying a schedule from a forum.
Not zinc in the nose. In 2009 the FDA warned about lasting loss of smell after intranasal zinc products, on the basis of more than 130 reports. That one is worth avoiding for a direct reason.
Vitamin C. Taken regularly, it does not make ordinary adults catch fewer colds. It does trim the length a little — about 8% in adults and 14% in children — and started after symptoms have already begun, it has shown no consistent benefit.
Garlic. One study, and not enough evidence to say anything either way.
Check interactions before you add anything. Supplements can interact with medications, and that is worth checking with a doctor or pharmacist: never mix supplements and medications on autopilot.
Spend the effort on what actually eases symptoms instead: rest, fluids, and the rest of the short list on what helps with a cold.

Homeopathy and what "not enough evidence" means

For Oscillococcinum, the homeopathic flu product that has a Cochrane review, a Cochrane review found no evidence that it prevents flu-like illness, and concluded that the treatment results may be explained by bias. The overall verdict is that there is not enough good evidence to draw a conclusion.

That phrasing matters. "Not enough good evidence" is not the same as "proven useless" — it means the studies that would settle the question have not been done, or have not been done well enough to count. It is a statement about the state of research, not a verdict on your experience.

When this is not the case

The vitamin C finding flips in one specific group: in people under heavy physical or cold stress — marathon runners, soldiers on exercise — regular vitamin C halved how often they caught colds. That group is defined by the studies, not by feeling tired at work.

And if you belong to a higher-risk group — 65 and older, infants and children under five (especially under two), pregnancy, chronic lung disease including asthma, heart disease, diabetes, chronic kidney disease, weakened immunity, a disability with underlying conditions, a BMI of 40 or above — the question is not which supplement to buy. It is how quickly you are seen, because flu and COVID treatment works best when it starts early: flu or COVID, when to test and treat.

Sources

Checked: September 6, 2026