Milk of Magnesia, used to solve problems of indigestion, ulcers and upset stomachs, has been banned, as it contains too much sulphate.
GlaxoSmithKline GSK stopped manufacturing the product last autumn but were allowed to sell their supplies, the Daily Express reported.
The stockpiles have gone so low that the bottles are being sold for up to 20 pounds, which is about 10 times their normal price, on eBay.
GSK is believed to be changing the recipe to comply with the EU limit.