If so, you may be eligible for the medical expense deduction. In total, you must spend more than 10% (7.5% if you are age 65 or older) of your Adjusted Gross Income (AGI) on medical expenses in order to possibly benefit from the tax break.on’t forget to include the cost of insulin and prescription drugs – but note that over-the-counter (OTC) medicines are not deductible. Perhaps somewhat surprisingly, OTC equipment and supplies can be deductible, however.