COHASSET, Mass. — When Rhonda Kallman set out to create a beer that would draw a crowd, she never expected the attention her Moonshot ’69 brew received this month.

The problem is that the light beer, made by Ms. Kallman’s company, New Century Brewing, contains caffeine. Earlier this month, she and three other manufacturers were told by the federal Food and Drug Administration that they must remove the stimulant from their beverages or stop selling them.

While most of the focus has been on two fruit-flavored, high-alcohol malt energy drinks, Four Loko and Joose, Ms. Kallman said her small company, which has suffered years of setbacks, is reeling from the news.

“This is Prohibition in 2010,” Ms. Kallman, 49, said. “It’s devastated the company, and as a U.S. citizen, I’m just flabbergasted.”