Pasted below is from Army Regulation 140-10. From what I read you will need to apply for a new commission so I would contact a Healthcare Recruiter for further directions.
Transfer Between Branches
3-1. Branch transfer
Branch transfer of officers is authorized between basic branches only. Officers requesting transfer to any of the special branches shown in
, below and the following require a new appointment:
(1) Between special branches.
(2) From a basic branch to a special branch.
(3) From a special branch to a basic branch.
The following are special branches of the Army. (All others are basic branches.)
(3) The AMEDD branches (Army Medical Specialist Corps (AMSC), Army Nurse Corps (ANC), MSC, Medical Corps (MC), Dental Corps (DC), Veterinary Corps (VC)).
Requests for branch transfer from ROTC officers who have not completed AD or RFD will be processed per
Constructive credit may be granted per AR 135-100, chapter 3
, for officers requesting appointment to a special branch.
Officers serving on AD in their Reserve commissioned status will be processed under AR 614-100,chapter 4
Transfer to an overstrength branch from an understrength branch will not be approved unless there are other overriding considerations.
Headquarters, Department of the Army will be informed of officers transferred to a Military Intelligence branch with AOC 35E or 35F. Send a copy of the orders to HQDA,
(DAMI-ZA), Washington, DC 20310-1000