An MD is a medical doctor who has completed medical school and residency training. A PA, or physician assistant (now officially being renamed “physician associate”), is a licensed medical professional who diagnoses illness, develops treatment plans, and prescribes medications, but follows a shorter training path and typically works in collaboration with a physician. Both can examine you, order tests, and manage your care, and you’re likely to see either one at a primary care office, urgent care clinic, or hospital.
How Their Training Differs
Becoming an MD requires four years of medical school after completing a bachelor’s degree, followed by a residency program lasting three to seven years depending on the specialty. A surgeon’s residency, for example, runs much longer than a family medicine residency. Only after finishing residency can an MD practice independently. The total timeline from college graduation to unsupervised practice is typically seven to eleven years.
PA programs are shorter. Most take about two and a half to three years and require at least a bachelor’s degree for admission. Students complete classroom coursework and a minimum of 1,600 clock hours of supervised clinical training across multiple medical specialties. Graduates earn a master’s degree. The entire path from college to clinical practice is roughly five to six years, about half the time it takes for most physicians.
Licensing and Certification Exams
MDs must pass all three steps of the United States Medical Licensing Examination (USMLE) to earn their license. These exams are taken during and after medical school, with Step 3 typically completed during residency.
PAs take the Physician Assistant National Certifying Exam (PANCE) after graduating from an accredited program. To maintain their certification, PAs must pass a recertification exam called the PANRE on a recurring basis. Both professions require ongoing continuing education to keep their licenses active.
What PAs Can and Cannot Do
In day-to-day practice, PAs perform many of the same tasks as physicians. They conduct physical exams, diagnose conditions, interpret lab results and imaging, create treatment plans, assist in surgery, and prescribe medications, including most controlled substances. For routine visits like managing high blood pressure, treating an infection, or stitching a wound, the care you receive from a PA looks nearly identical to what you’d get from an MD.
The key difference is prescribing authority for certain controlled substances, which varies by state. In Arkansas, PAs can only write a five-day prescription for opioids or prescribe stimulants originally started by a physician. In Florida, PAs are limited to a seven-day supply of the most tightly regulated controlled substances. Massachusetts requires a supervising physician to review any PA-written prescription for these drugs within 96 hours. These restrictions don’t apply to the vast majority of medications PAs prescribe daily.
How PAs and Physicians Work Together
Early PA laws framed the relationship as a strict supervisor-employee dynamic. That model has largely evolved. The American Academy of Physician Associates (AAPA) now describes the working relationship as collaborative rather than supervisory, meaning PAs make autonomous decisions about patient care and consult a physician when a case exceeds their expertise, much like any provider would refer a patient to a specialist.
The exact arrangement depends on state law. Some states still require a formal supervisory agreement with a named physician, while others have moved toward collaborative practice models that give PAs more independence. Regardless of the legal framework, in practice, PAs and physicians on the same team communicate regularly and share responsibility for patient care.
Specialty Flexibility
One of the most distinctive features of the PA profession is lateral mobility across specialties. Because PA training covers a broad medical foundation rather than a single specialty, PAs can transition from, say, orthopedics to cardiology or emergency medicine without completing a new residency. A 2024 study in BMC Health Services Research confirmed that PAs navigate across various specialties throughout their careers, usually without additional formal education. Physicians, by contrast, are locked into the specialty they chose for residency. Changing specialties as an MD typically means completing an entirely new residency program, which can take several more years.
Quality of Care Compared
Research consistently shows that patient outcomes are comparable whether care is delivered by a PA or a physician. A rapid review published in PMC found no difference in patient satisfaction between PAs and physicians overall. In primary care studies focused on diabetes management, patients treated by PAs had similar blood sugar control, blood pressure, and cholesterol levels as those treated by physicians. One emergency department study actually found statistically higher satisfaction scores for PAs than for physicians, with PAs scoring 9.3 out of 10 compared to 9.0 for physicians.
These findings don’t mean PAs and MDs are interchangeable in every clinical situation. Complex, rare, or high-acuity cases generally require the deeper specialty training that physicians bring. But for the conditions most people seek care for, the evidence suggests you’re in equally capable hands with either provider.
How Billing Works
When a PA provides care under a physician’s direct supervision and the visit is billed under the physician’s name, Medicare reimburses at 100% of the standard physician rate. When the PA bills independently under their own name, Medicare pays 85% of the physician rate. This distinction matters more to the business side of a medical practice than to you as a patient. Your copay and out-of-pocket costs are generally determined by your insurance plan, not by whether an MD or PA saw you.
The Name Is Changing
In 2021, the AAPA voted to change the profession’s official title from “physician assistant” to “physician associate.” The word “assistant” has long been a sore point, as it implies PAs simply follow orders rather than exercise clinical judgment. Oregon became the first state to adopt “physician associate” in its laws, followed by Maine and New Hampshire. As of now, 39 of the AAPA’s 125 constituent organizations have completed their own title change efforts. You may see either term used depending on where you live, but they refer to the same profession and the same credentials.