4 Things to Know About Zinc And Your Cold

Zinc is often touted as a way to fight the common cold. But while research suggests it does work, there are some caveats. Tod Cooperman, MD, president of the independent testing group ConsumerLab.com, provides the scoop:

Zinc helps treat—not prevent—a cold

Popping zinc within 24 hours of the start of symptoms helps shorten your sniffle, according to a 2013 Cochrane review. The authors say significant effects were seen at doses of at least 75 mg (the equivalent of three or four lozenges) per day, taken as long as your cold lasts. How does it work? The theory, according to the Mayo Clinic, is that zinc may keep cold viruses from multiplying and taking up residence in your nose and throat. But don’t bother taking it just to take it; there’s no evidence it’ll actually prevent a cold.

Read more: Best and Worst Foods to Eat When You’re Sick

Pick a lozenge, not a spray

Back in 2009, the U.S. Food & Drug Administration warned against using zinc gel sprays and nasal swabs after receiving more than 130 reports of people losing their sense of smell after using these products. (The manufacturer pulled the products from store shelves, though they claim no link has been established.)

Though you can no longer buy zinc nasal spray, it’s still available as a throat spray, which might be problematic, according to Dr. Cooperman. “If you spray it into your throat it can still go up your nose,” Dr. Cooperman says.

The best way to go is still the good old lozenge. Just make sure you suck—not crunch—it: “It needs to dissolve slowly to be effective so it can coat your throat,” explains Dr. Cooperman.

Read more: Best and Worst Exercises to Do When You Have a Cold

Not all lozenges are created equal

In order for a lozenge to provide enough zinc to be effective, it needs to contain between 13 and 23 milligrams, Dr. Cooperman says. Yet only two of the four lozenges Consumer Lab tested—Cold-Eeze Homeopathic Cold Remedy and Nature’s Way Zinc—provided enough. (There are other brands of zinc they didn’t test.)

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You can’t pop ’em like candy

The safe upper limit for zinc in adults is 40 milligrams per day, as determined by the Institute of Medicine. While it’s okay to exceed that 40mg limit for three to five days (or roughly the length of a cold), you still don’t want to down the lozenges like crazy. At most, only take one every three hours if you’re sick, and limit yourself to one a day if you’re healthy: “Too much zinc can actually depress your immune system,” explains Dr. Cooperman.

Read more: How to Stop a Cold In Its Tracks

This article originally appeared on Health.com.