Yes, per IRS Publication 502, you can deduct Medicare Part D if you itemize your deductions.
Also see this TurboTax Help Article: How does the standard deduction differ from itemizing deductions?
The premiums you paid for Medicare Part D are a medical expense.
If you had the premiums taken out of your Social Security benefits, and you entered it on the screen where you entered your SSA-1099, TurboTax will automatically include it in your medical expenses. You do not enter it anywhere else.
If you did not have the premiums taken out of your Social Security benefits, you can include it in the insurance premiums that you enter when you enter your medical expenses.
But only medical expenses in excess of 7.5% of your Adjusted Gross Income (AGI) are deductible. (Enter the full amount that you paid in TurboTax. TurboTax will subtract 7.5% of your AGI.) If your total medical expenses, including the Medicare Part D premiums, are less than 7.5% of your AGI, the Part D premiums will not make any difference in your deductions or your tax.
In addition, medical expenses are an itemized deduction. They will not reduce your tax or increase your refund unless your total itemized deductions are more than your standard deduction.