You can use money in an FSA or HSA tax-free for prescription drugs, but you can no longer use it for over-the-counter drugs that have an active medical ingredient without a prescription. (There are exceptions for insulin, glucosamine and chondroitin supplements that are used for arthritis treatment, and prenatal vitamins, says Jeremy Miller, CEO of FSAStore.com, which specializes in selling items that are FSA-eligible.) But if you get a prescription, such as for pain relievers or allergy medications, the cost is an eligible expense.