Looking for a quick pick-me-up to get through a long afternoon? Forget that cola. A fizzy citrus drink could provide even more of a boost.

A new study shows that citrus-flavored sodas often have a higher caffeine content than the most popular colas. The research also found that caffeine content can vary widely from brand to brand, and even within a brand.

The researchers — along with consumer advocates — say labels on packaging should give the caffeine content to help buyers make informed choices. While most cans and bottles of soda don’t give caffeine amounts, some national brand beverage companies are already heading in that direction.

“I don’t really take a stand on whether caffeine is good or bad, but I do think the consumer has a right to know what they’re getting,â€Â said Leonard Bell, one of two food researchers who conducted the study at Auburn University.

Food and Drug Administration spokeswoman Veronica Castro said a 0.02 percent caffeine content is generally recognized as safe for cola-type beverages.

For a 12-ounce soft drink, that̢۪s about 72 milligrams of caffeine.

The study by Bell and co-author Ken-Hong Chou found caffeine content in 12-ounce sodas ranged from 4.9 milligrams for a store brand of cola to 74 milligrams in Vault Zero, a citrus drink.

Rather than deterring shoppers, labeling might have the opposite effect on those seeking more caffeine, he said.

The Coca-Cola Co., based in Atlanta, and Purchase, N.Y.-based PepsiCo Inc. said they are phasing in new labels that include caffeine content. Most national brands also provide lists of the amount of caffeine in their products on their Web sites.

“It’s really in our best interest and that of our consumers to provide that info,â€Â said Diana Garza, a Coca-Cola spokeswoman.

Bell and Chou say the buzz caused by caffeine is its main draw.

Their study analyzed the caffeine contents of 56 national brand and 75 store brand carbonated drinks. It was published in the August issue of the Journal of Food Science.