 After completing a four-year Bachelor of Science in Nursing (BSN), a Psychiatric Mental Health Nurse Practitioner degree requires two to five additional years of training.At minimum, the candidate must complete an approved Master's of Science in Nursing (MSN) or Doctor of Nursing Practice (DNP) advanced nursing education program.Individuals who already have a bachelor's degree in another field can attend one of many accelerated BSN programs before entering an approved MSN or DNP program.