“Nighttime.” “Non-Drowsy.” “Maximum.” When you see those terms on over-the-counter drugs, you naturally assume they have a uniform meaning. Turns out, they don’t.

The Food and Drug Administration says it has no set definition for these kinds of descriptions. That means drugmakers can improvise.

Some CR secret shoppers told us they found terms like these confusing. Barbara Young, Pharm.D., of the American Society of Health-System Pharmacists (ASHP), agrees: “These claims are basically advertising copy—meant to catch your eye.”

We took a look at a few common ones to see what they might mean.

SPECIAL REPORT: HOW TO TREAT A COLD OR THE FLU

Severe
This suggests that a manufacturer added an ingredient—though which one varies. Vicks DayQuil Severe Cold & Flu, for example, contains the cough medicine guaifenesin, and the regular version does not. But with Vicks NyQuil Severe, the difference-maker is phenylephrine, a decongestant.

Express, Fast
It’s hard to make sense of these terms. For example, Theraflu puts “ExpressMax” on all its products other than hot-drink powders. And Mucinex put “Fast-Max” on all its multi-symptom products, though nothing in the packaging explains how the products work faster. “These terms are used to market the product,” says the ASHP’s Young.

Non-Drowsy, Daytime
This can suggest that a product doesn’t contain a sleep aid, as in the case of Contac Cold + Flu Day. But it can also mean that a product includes a stimulant, such as pseudoephedrine in Advil Cold & Sinus Non-Drowsy.

Day/Night, 24-Hour
“Day/Night” often indicates a combo pack, a regular version for day and another with a sleep aid for night. “24 Hour” could mean that the product has double the dose: Sudafed 24 Hour, for example, has 240 mg of pseudoephedrine, a decongestant, and Sudafed 12 Hour has 120 mg.

Night, Nighttime, PM
These terms often indicate that a product uses an antihistamine with drowsiness as a side effect. But different brands use different sleep aids: Alka-Seltzer Plus Maximum Strength Night Cold & Flu relies on doxylamine, and Tylenol PM opts for diphenhydramine. (Read more about sleeping pills.)

Maximum, Extra Strength
This can mean that a drug has a higher dose of at least one listed drug—but not necessarily all its active ingredients. For example, Robitussin Maximum Strength Cough + Chest Congestion DM has twice as much guaifenesin as its regular version—but both versions have the same amount of dextromethorphan. And a higher dose isn’t always needed—and often poses greater risks.

Editor’s Note: This article also appeared in the January 2018 issue of Consumer Reports magazine.