GlaxoSmithKline's diet pill, alli, is now back in most U.S. stores. The British drugmaker voluntary recalled the product last March after finding some packages in stores didn't contain real alli, indicating tampering after shipment. The Food and Drug Administration is still investigating. Glaxo's innovation center for consumer products, in Parsippany, New Jersey, says the product package was redesigned to make tampering easier to spot. Before shipping alli, known chemically as orlistat, to retail stores, Glaxo launched it in mid-February through Drugstore.com and other online retailers. Since late January, it's been available for preorders on Amazon.com, where Glaxo says it was the top-selling diet item during the first pre-order week. GlaxoSmithKline says alli is the only nonpresciption diet medicine approved in the U.S. that's proven to help people lose weight.