The Bottom Line
There’s no convincing evidence that any supplement can prevent or treat colds. “Cold remedies,” including many over-the-counter drugs, may well make you feel better, since they have a strong placebo effect. That is, if you expect or hope that a remedy is going to help, there’s a fair chance it will, whether it contains vitamins, herbs or just plain old sugar. And, of course, remedies may seem to work because colds go away on their own. Though we don’t recommend them, it probably can’t hurt to take such products when you feel a cold coming on, but taking them throughout cold season, as is sometimes recommended, increases the risk of adverse effects.