If I used an early IRA withdrawal to pay medical premiums (I have been paid as a 1099, not an employee), may I enter those premiums under "medical expenses?"

Are you asking if you can use that as an exception to the 10% early withdrawal penalty for the IRA distribution?
Maybe - if it was to pay medical insurance premiums during a period of unemployment.

Yes, you may enter them under medical expenses.  However, you may qualify for self-employed health insurance deduction, which is a much better benefit for you. You can deduct the premiums as self-employed (SE)  insurance deduction - if a policy is either in the name of the business or the individual owning the business (you). The deduction is limited to the smaller of:

• your premiums paid or 
• your net profit from your business (gross business profit minus your business expenses)

If you do have net profit, you may enter your medical premiums when going through your business expenses...

If you don't qualify, or if there's a remaining amount that doesn't qualify due to your net profit, then that amount is entered as medical expenses in Deductions & Credits:

1. Federal Taxes
2. Deductions and Credits
3. Scroll down to Medical, select Medical Expenses - follow the prompts, enter total insurance premiums amount (that you have not deducted as SE deduction)