The 'Plan B' morning-after birth control pill won't be hitting pharmacy shelves anytime soon, following a surprise block by the nation's health secretary.

Health and Human Services Secretary Kathleen Sebelius overruled her own experts at the Food and Drug Administration who had called for lifting the age limit of 17 for the contraceptive, allowing people of any age to buy it without a prescription.

The drug's maker did not sufficiently show that younger girls will understand how the product is used, without guidance from an adult, Sebelius reasoned.

"I do not believe enough data were presented to support the application to make Plan B One-Step available over-the-counter for all girls of reproductive age."

The decision was a shocker for manufacturer Teva Pharmaceuticals, and puts a crimp in its plans to have the pills more readily available over-the-counter.