Qualified medical expenses are defined under IRC 213(d). Eligible expenses include, but are not limited to, out-of-pocket costs under your health insurance plan, such deductibles, coinsurance, and copays.
These medical expenses must be primarily for treating or preventing a physical or mental disability or illness. They don't include expenses that are merely beneficial to general health, such as vitamins, nutritional supplements, fitness club memberships, or vacations.
Use your HSA to pay for or reimburse yourself for costs you pay for diagnostic services, imaging, lab fees, primary care visits, prescription drugs, physical therapy, durable medical equipment (wheelchairs, lifts, hospital beds, oxygenators, etc.,)
Qualified medical expenses also include many medical expenses that aren’t normally included under your major medical insurance policy at all, such as chiropractic care, some alternative medicine, the cost of transportation to medical appointments, eyeglasses, and hearing aids.
Exception: You generally cannot use your HSA money to pay your medical insurance premiums (unless you’re receiving federal unemployment compensation). But your medical insurance premiums may be a tax-deductible expense, anyway.
Note that while vitamins and nutritional supplements are not eligible if taken for the purpose of maintaining your general health, they would be qualified expenses if prescribed by a health care professional for the purpose of treating or maintaining a specific medical condition.
For a complete list of qualified medical expenses, see IRS Publication 502