Fruit-flavored e-cigarettes recently authorized by the Food and Drug Administration were not significantly better at helping smokers quit than tobacco-flavored e-cigarettes, according to a new memo that's likely to stir new 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.