Yes. However, once you start treating a patient you have a responsibility to not "abandon" that patient. The two requirements that must be met in terminating the physician/patient relationship to avoid abandonment are: (1) you must provide proper and adequate notice to the patient; and (2) the patient must be able to secure another doctor to replace you. (The latter requirement may be difficult to fulfill if your practice is located in a rural area or your specialty is unique to an area, in which case you may be forced to continue treatment.)
Be advised that you are allowed to terminate a patient relationship for any reason. It is advisable to ensure that you communicate clearly with the patient should you wish to terminate the relationship and to keep well-documented notes of your discussions with the patient prior to termination, especially if you are terminating the relationship due to the patient's inability to pay, failure to keep appointments or failure to follow medical advice.