In IRS Publication 502, "Medical and Dental Expenses," see "Dependent" under "Whose Medical Expenses Can You Include?" It explains exceptions that, in certain cases, allow you to deduct medical expenses you paid for someone who is not your dependent. You can read it online at the first link below, or download the PDF of the publication from the second link. "Whose Medical Expenses Can You Include?" is on page 3.
Whose Medical Expenses Can You Include? - Dependent
Publication 502, Medical and Dental Expenses (PDF)
