Functional medicine is a real, organized approach used by licensed clinicians, but the evidence for it as a whole is thin. The best-known study, from Cleveland Clinic in 2019, was observational: functional medicine patients reported a larger gain in physical health at six months than similar primary care patients, but by 12 months the difference wasn't significant. We found no randomized trial or systematic review that tests the model as a whole, and some lab tests common in functional medicine have weak validation. Whether it's worth trying depends on who is practicing it, what they test, and what they charge.
What functional medicine is
The Institute for Functional Medicine (IFM) describes functional medicine as an approach that treats the "root causes" of disease. It uses each person's genes, environment and lifestyle to work out what is driving their symptoms (IFM). That is IFM's own description, not an independent assessment.
It isn't a license or a medical specialty. MDs, DOs, naturopathic doctors, nurse practitioners, chiropractors, dietitians and other licensed clinicians can train in it. IFM states that its certification doesn't change anyone's scope of licensure or give them added legal or specialty status (IFM eligibility). For how the credentials compare, see naturopath vs functional medicine doctor.
What the evidence shows
The Cleveland Clinic study (2019)
This is the study supporters cite most often (Beidelschies et al., JAMA Network Open, October 2019). Researchers looked back at records from 2015 to 2017 and compared patients at the Cleveland Clinic Center for Functional Medicine with similar patients at a family health center.
| What was measured | Functional medicine | Family health center | Difference significant? |
|---|---|---|---|
| Change in self-reported physical health score at 6 months (398 matched pairs) | +1.59 | +0.33 | Yes |
| Same score at 12 months (220 per group) | +1.60 | +1.09 | No |
What to keep in mind:
- It was observational. Patients chose their care. They weren't randomly assigned.
- The outcome was self-reported quality of life, measured with a standard questionnaire (PROMIS). The study didn't measure clinical outcomes such as blood pressure control or complications.
- The authors called it exploratory. They didn't adjust for multiple comparisons, many eligible patients were dropped during matching, fewer people responded at 12 months, and the authors said prospective studies are needed.
- Some authors had ties to the field. Two worked at the Center for Functional Medicine, and one reported being a paid educational consultant for IFM.
Critics add that the functional medicine patients were more affluent and that the 6-month gain was small (Gorski, Science-Based Medicine, 2019). IFM, in turn, presents the study as evidence that the model improves patient outcomes (IFM).
Controlled trials and reviews
Our searches found no randomized controlled trial or systematic review that tests functional medicine as a complete model of care. They found trials of individual parts, such as specific diets, supplements or acupuncture, and a 2024 trial of functional medicine health coaching (Medicine, 2024). Evidence that one part helps doesn't show that the whole approach works. These were web and PubMed-indexed searches, not a full systematic review, so treat the result as "none found" rather than "none exist."
The American Academy of Family Physicians (AAFP) reviewed the evidence in 2014 and 2016 and found it insufficient to support functional medicine in family medicine; it judged some claims potentially dangerous. In 2018 it lifted its ban on functional medicine continuing-education credit, but only for overview sessions. "How-to" sessions remain ineligible (AAFP, March 2018).
The main criticisms
Lab tests with weak validation
Critics say functional medicine orders many tests whose meaning is unclear (Gorski, 2016). For several popular tests, mainstream guidance supports that concern:
| Test | Often offered for | What the guidance says |
|---|---|---|
| Food-specific IgG blood panels | "Food sensitivities" | A 2022 scientific short from the Association for Diagnostics & Laboratory Medicine (ADLM) says food-specific IgG has not been shown to be valuable for diagnosing food allergy, citing the 2014 US allergy practice parameter among its sources. Positive results can occur in healthy people. Allergy societies in Europe (EAACI, 2008) and Canada (CSACI, 2012) have also advised against using food-specific IgG tests to diagnose food reactions. |
| Saliva or blood "adrenal fatigue" tests | Tiredness, stress | The Endocrine Society says there's no scientific proof adrenal fatigue is a real condition and no test can detect it (updated January 2022). |
| Reverse T3 | Thyroid symptoms | Rated not useful for routine thyroid testing in ADLM's lab-use guide. See functional medicine for thyroid. |
| Urine organic acid panels | Nutrient status, metabolism, gut | Urine organic acid tests have been validated for diagnosing inherited metabolic disorders (2016 quality-assurance study). We found no independent study validating commercial functional or wellness panels. Labcorp says its own urine organic acid test has not been cleared or approved by the FDA and may miss some disorders (Labcorp). |
They aren't cheap. At one large practice, specialty tests cost about $400 each and typically aren't covered by insurance (Parsley Health).
Supplements and cost
Supplements are often part of a functional medicine plan, and they add up. Parsley Health, for example, puts supplements at $30 to $100 a month on top of membership and labs (Parsley Health). The IRS doesn't treat supplements as medical expenses unless they're recommended for a specific condition a physician has diagnosed (IRS Publication 502). IFM itself won't count training from companies whose main business is selling health products toward certification (IFM). If a practitioner sells supplements in the office, ask whether you can buy the same product elsewhere.
The broader critique
The sharpest critics, such as David Gorski of Science-Based Medicine, call functional medicine the worst features of conventional medicine combined with unproven treatments (Science-Based Medicine, 2016). Supporters point to the Cleveland Clinic study and to the model's focus on lifestyle, environment and each person's biology (IFM). The fair summary is that the approach hasn't been tested the way most medical treatments are, and the quality of care depends heavily on the individual clinician.
How to vet a functional medicine practitioner
- Check the license, not just the credential. Ask what license they hold (MD, DO, ND, NP, PA, DC, RD or another) and in which state, then look it up. In New York, use NYSED license verification.
- Ask about functional medicine training. The current IFM credentials are FMCP-M (for MDs, DOs, NDs, NPs and PAs) and FMCP (for other licensed clinicians). The older "IFMCP" title is being phased out (IFM).
- Ask about each test before you agree to it: what it's for, what it costs, whether insurance covers it, and how the result would change your plan.
- Ask about supplements: which ones, what evidence supports them, whether they interact with your prescriptions, and whether you can buy them elsewhere.
- Ask about cost up front: visit fees, program fees, refund policy, and what's included.
- Ask how they work with your other doctors: will they send results to your primary care doctor, and when do they refer back?
Red flags
- A diagnosis of "adrenal fatigue" based on a saliva or blood test.
- A food-IgG panel used to diagnose food sensitivities.
- Advice to stop or change a prescribed medicine without involving the doctor who prescribed it.
- Promises to cure or reverse a chronic disease.
- Pressure to prepay a large program at the first visit.
- A practitioner who can't tell you which license they hold.
Who might reasonably try it
If you've had a standard medical workup and want a clinician who focuses on diet, stress and lifestyle, a functional medicine practitioner may suit you. The lower-risk route is a licensed clinician who orders tests one or two at a time, explains the evidence plainly, gives you prices in writing, and keeps your primary care doctor informed. Costs vary widely; see functional medicine cost and insurance.
What to do next
- Browse functional medicine doctors and check the license each one lists.
- Prefer an MD- or DO-led approach that combines conventional and complementary care? See integrative medicine doctors and integrative vs functional medicine.
- Comparing with naturopathy? See naturopathic doctors in our directory and what the evidence says about naturopathy.
When to see a medical doctor: for new, severe or worsening symptoms, see a medical doctor first. If a functional medicine practitioner finds an abnormal result, take it to your primary care doctor or the right specialist.
Last reviewed: October 2026