Fruit-flavored e-cigarettes recently authorized by the United States Food and Drug Administration (FDA) were not significantly better at helping smokers quit than tobacco-flavored e-cigarettes, according to a new memo that's likely to stir more questions about the agency's decision.

The FDA last month gave its first OK to fruit-flavored vapes – essentially endorsing them as a less-harmful alternative to traditional cigarettes. The decision came despite the agency's longstanding position that such flavors appeal to children and must show extra health benefits to warrant approval for adults.

Health groups and Washington lawmakers quickly condemned the decision and have called for an explanation.