yes, you can buy over the counter meds but need to have a prescription (yes, for a non-prescription item) for tax purposes. Here's the notice from my Bank of America HSA.
Eligible Medical Expenses that Require a Prescription
Starting January 1, 2011, OTC medicines or drugs can be reimbursed only if prescribed by a doctor. For these items to be
eligible medical expenses reimbursable from your health benefit account, you will need a valid prescription from your doctor.***
• Acid controllers
• Allergy and sinus medicine
• Anti-diarrheals
• Anti-gas products
• Anti-itch and insect bite
• Anti-parasitic treatments
• Antibiotics
• Baby rash ointments/creams
• Cold sore remedies
• Cough, cold and flu
• Digestive aids
• Feminine anti-fungal/anti-itch
• Hemorrhoidal preps
• Laxatives
• Motion sickness
• Pain relievers (for example, aspirin)
• Respiratory treatments
• Sleep aids and sedatives
• Stomach remedies