What is functional medicine? A plain-language guide to the evidence

Functional medicine is a model of care that the Institute for Functional Medicine (IFM), founded in 1991, describes as a systems biology–based approach that focuses on identifying and addressing the root cause of disease. Instead of starting from a single diagnosis, the practitioner maps how your history, diet, sleep, movement, stress, relationships, genes and environment may be shaping how you feel.

Cleveland Clinic, which runs a Center for Functional Medicine, says the foundation of the approach is using food as a first-line therapy, and that its program looks at lifestyle influences, genetics and the environment. If the food side interests you, read about functional nutrition.

In practice, first visits tend to be long and detailed: in the Cleveland Clinic study described below, the first functional medicine visit lasted 60 to 75 minutes. Plans usually center on food, movement, sleep and stress, and sometimes add lab tests and supplements.

It is not a medical specialty. The American Board of Medical Specialties (ABMS) has 24 member boards, from family medicine to urology, and none of them is for functional medicine (or for integrative or lifestyle medicine). Certificates in functional medicine come from private organizations, IFM among them; a certificate is training, not a license to practice medicine.

Who practices it varies. Medical doctors, nurse practitioners, chiropractors, naturopaths, dietitians and health coaches can all use the label. What each may legally do (diagnose, prescribe, order tests) depends on their own license.

It is not the same as naturopathy, although the two overlap. The National Center for Complementary and Integrative Health (NCCIH) notes that “functional medicine” sometimes means something close to integrative health and sometimes more closely resembles naturopathy. Naturopathy is a separate system with 19th-century European roots; licensed naturopathic physicians (ND or NMD) train at accredited naturopathic schools, and licensing rules vary by state and territory.

The lifestyle parts stand on solid ground. CDC says most chronic diseases, such as heart disease, cancer and diabetes, stem from a short list of risk factors: smoking, poor nutrition, physical inactivity and excessive alcohol use. Better food, movement, sleep and stress habits are worth working on with any clinician.

Research on the model itself is thin. The best-known study (Beidelschies and colleagues, JAMA Network Open, 2019) looked back at the records of 7,252 adults at Cleveland Clinic. In matched groups, patients seen in functional medicine improved a physical health score by 1.59 points at six months, versus 0.33 points at a family health center; at 12 months the difference was no longer significant. The authors called the work exploratory: it was observational, at one center, with many patients missing follow-up, so it cannot show cause and effect.

Specialty tests are where caution matters most. Some popular panels have not been validated to diagnose disease. For example, the American Academy of Allergy, Asthma & Immunology (AAAAI) warns that IgG “food sensitivity” tests do not reliably identify problem foods. See which tests are worth it in functional medicine labs.

The same goes for cleanses: there is no good evidence that detox products remove toxins from the body; your liver and kidneys already do that work.

Functional medicine cost varies by practice. Coverage depends on the practice and on your plan, and some practices do not bill insurance at all. Even where visits are covered, specialty labs and supplements can be billed separately.

Does insurance cover functional medicine? Sometimes, in part. Cleveland Clinic, for example, says its functional medicine physician visits are covered by most insurance plans except Medicaid and Medicaid HMOs; nutritionist visits depend on your plan; some specialized lab tests may be covered; supplements are an extra cost; and it says virtual follow-up visits with its functional medicine team are not covered by insurance.

Before you book anywhere, ask: are you in network with my plan, what does the first visit cost, which tests are included and which are optional, and will I get an itemized receipt (a superbill) to submit to my plan? If you hope to use an HSA or FSA, check with your plan administrator first.

The Health Initiative (THI) is the nonprofit that runs this telehealth clinic. Dr. Diana Nieves Castro is a general practice physician licensed in Puerto Rico; she is not a functional medicine specialist, and THI does not offer functional medicine as a service.

At THI’s in-person medical and wellness retreat in Puerto Rico, she provides all the medical care with a root-cause approach led by a licensed physician: a physician assessment and labs when clinically appropriate, with education on habits. It is wellness and habits work, not a cure for any condition.

Before you choose any retreat, read what to ask any retreat about its medical care, and see what to expect at the retreat.

In Puerto Rico, you can also see her for primary care or book an online visit; online visits are only for people who are physically in Puerto Rico. Learn more about Dr. Nieves Castro.