assuming what you're paying off are qualified medical expenses the payments are deductible in the year paid on schedule A. they'll only benefit you if, after the reduction by 7.5 % of adjusted gross income, the remainder + your other itemized deductions exceed your standard deduction.
Medical expenses are eligible to be claimed as itemized deductions when you pay the provider. If you paid the provider all at once from a loan, that's when you deduct the expense, not when you pay off the loan. But if you are paying the provider over time, you can deduct what you pay as you pay it.
You can't deduct amounts reimbursed by insurance or other tax-free sources like an FSA or HSA. And you can deduct expenses you paid for yourself, your spouse, and your dependents.