The over-the-counter drug comes in a turquoise blue capsule with a dark blue band and the text "60 Orlistat." However, people in seven states have reported finding tablets and capsules of various shapes and colors in the bottles, the British drugmaker said Thursday.
Those states include New York, Texas, Florida, North Carolina, Louisiana, Alabama and Mississippi.
There are also reports that the tamper-resistant seals on some bottles are not authentic. Alli comes in bottles with an inner foil barrier labeled "Sealed for Your Protection."
Some bottles are missing their labels as well.
The drugmaker is still trying to determine what the foreign pills and tablets are.
GlaxoSmithKline has received information about 20 tampered Alli bottles so far, but no related reports of serious illnesses.
The company is asking pharmacies and retailers in the United States and Puerto Rico to immediately remove the drug from store shelves.
Customers who have questions can call 800-671-2554.