You must have an official doctor-issued diagnosis of celiac disease or non-celiac gluten sensitivity, plus a doctor-written prescription stating that your gluten-free diet is necessary to treat your condition. 

You may deduct the cost of gluten-free (GF) food that is in excess of the cost of the gluten containing food that you are replacing. For example, if a loaf of gluten-free bread costs $5.00 and a comparable loaf of gluten containing bread costs $2.50, you may include in your medical expenses the excess cost of $2.50. The full cost of special items needed for a GF diet may be deducted.  Be sure to keep receipts or other proof.

Only the amount of your Medical expenses that are in excess of 7.5% of AGI qualify as an itemized deduction, and your total itemizeds must be in excess of the new, higher Federal Standard deduction..

State taxes may be different.