That is hardly surprising, because 5-Hour Energy does not contain sugar.

Asked whether consumers mistakenly believe that the shot does not produce a caffeine-related crash, Ms. Lutz said that the use of the special mark and its explanation were clear. “I don’t believe that it is misleading,” said Ms. Lutz, who added that the advertising division of the Council of Better Business Bureaus had approved the “No Crash Later” claim.

She added that another study showing the benefits of 5-Hour Energy was undergoing “peer review” for possible publication in a scientific journal. But she declined to say why the results of the study, which was apparently conducted five years ago, had not yet appeared. That study found a benefit when 5-Hour Energy was compared to a placebo like flavored water, she said.

Whatever the case, the energy drink boom has come full circle in Asia, the region where it started. Over the last decade, sales of Lipovitan D have fallen and its maker, Taisho Pharmaceuticals, has tried various strategies to revitalize the brand. Among them: bringing out Lipovitan Junior, a caffeine-free version for children.

In Thailand, Krating Daeng has suffered a similar fate. Its producer has tried to freshen up that brand by proclaiming that the Vitamin B12 in it “helps the functions of the nervous system and brain.”

Last year, the Foundation for Consumers in Thailand, an advocacy group, started a publicity campaign against energy drinks like Krating Daeng, arguing that producers were promoting unfounded health claims to push caffeine.

“This product just needed a way to add value to extend its life cycle,” said Patchara Klaewkla, an official at the foundation. “This product has been in the market for a long time.”