Functional Medicine: What the Evidence Shows and What Critics Say
A neutral look at the published studies of functional medicine care, what supporters and critics each argue, and which parts are evidence based and which are not yet shown.
Content last updated . This page has not been medically reviewed.
Information only, not medical advice. For emergencies call 911 (in the US). Serious or worsening symptoms need a doctor first. Do not stop or change prescribed medicines because of anything you read about a care model.
What "evidence" means here
Functional medicine is a whole model of care (see what it is and how it works), so there are two separate questions. Do the individual parts, such as diet quality, activity, sleep and stress reduction, help? And does the packaged model help more than usual care? Reviewers on both sides agree the first can be yes. A 2026 review by Yale and NYU authors says many interventions used in functional medicine "are evidence based" but that evidence validating it as a distinct model "remains limited". [1]The studies we found
We searched PubMed on 2026-10-22 for "functional medicine" in titles combined with trial, randomized, systematic review and related terms. Studies are listed with design, size and who ran them.| Study | What it found | Label |
|---|---|---|
| Cleveland Clinic retrospective cohort, 7,252 patients (authors work at the clinic's functional medicine center) [2] | At 6 months, functional medicine patients improved 1.59 points on a physical-health score versus 0.33 in primary care patients (398 matched pairs). The difference was not significant at 12 months. The authors called for prospective studies. [2] | Promising but limited: not randomized, one site |
| Open-label randomized pilot in type 2 diabetes (Cleveland Clinic), 71 randomized, 47 finished [3] | Adding a functional medicine approach to usual care gave no significant improvement in blood sugar, metabolic or quality-of-life outcomes. The main goal was met by 15.8 percent versus 11.1 percent (p = 0.68). [3] | No benefit shown in a small pilot |
| Randomized trial of health coaching with an elimination diet, 125 health workers (authors include Institute for Functional Medicine staff) [4] | No between-group differences in the primary analysis. Both groups improved, and people with more symptoms at the start did better with coaching in a subgroup analysis. [4] | Mixed; subgroup finding is exploratory |
| Vanderbilt program for inflammatory bowel disease, 19 enrolled, 15 finished, no comparison group [5] | Questionnaire scores improved; every person who finished also lost weight. [5] | Insufficient evidence |
| George Washington University case series, 51 people with mild cognitive impairment or early Alzheimer's disease [6] | Results were summarized without formal statistics, and 29 of 51 stopped within a year, most often for cost, complexity or lack of caregiver support. [6] | Insufficient evidence |
Two design points matter. The diabetes pilot was open-label, and in a coaching versus self-guided diet comparison people are unlikely to be unaware of which group they are in, which leaves room for expectation effects. A critic made a related point in 2017, that the Cleveland Clinic trials compare usual care alone with usual care plus functional medicine. [7]
Whole-model systematic review or large multi-site randomized trial: Proper evidence not found. The title searches returned one-site cohorts, pilots, case series and narrative reviews, and an editorial arguing for broader definitions of evidence. We did not find a systematic review of the whole model.
What supporters argue
Supporting clinics describe the model as personalized and aimed at underlying causes, and report patient-reported gains in their cohorts. [8] [2] The Cleveland Clinic authors say their results show beneficial associations but that prospective studies are needed. [2]What critics argue
- Definition. A 2017 Science-Based Medicine commentary says the model's principles are poorly defined and that it adds lifestyle advice to a lot of testing. [7]
- Testing and cost. The Yale and NYU review says its diagnostic strategies "may contribute to low-value testing, care cascades, and health inequities" through out-of-pocket costs. [1]
- Standards. The same authors argue new clinical frameworks should meet the same standards of evidence as the rest of medicine. [1]
- Institutional caution. The American Academy of Family Physicians reviewed the literature in 2013 and found "there wasn't sufficient evidence" to award credit for functional medicine education, then in 2018 allowed credit for overview activities but not for teaching clinicians to perform its techniques. [9]
The Institute for Functional Medicine's own responses were not readable (its pages returned HTTP 403), so its current position is not summarized here. Authors of some trials are affiliated with the institute or the clinic that offers the service, as noted in the table.
How to read the claims
Ask whether a claim is about the whole model or about a part (for example lifestyle change), whether the study had a comparison group, and who ran it. See understanding evidence and how to evaluate a proposed treatment plan. Related: integrative, functional and lifestyle medicine.Frequently asked questions
Is functional medicine evidence based?
Parts of it are, such as nutrition, exercise, sleep and stress management, according to a 2026 review; the evidence for it as a distinct model remains limited. [1]
Has a randomized trial tested functional medicine?
Yes, small ones. A diabetes pilot found no significant benefit over usual care, and a coaching trial found no overall difference between groups. [3] [4]
Why do the studies show improvement if the evidence is limited?
In the cohort and case-series designs there was no randomized comparison, so improvement may reflect other factors. The Cleveland Clinic authors called for prospective studies. [2]
What do critics say?
They describe the model as loosely defined, test-heavy and costly, and call for the same evidence standards as the rest of medicine. [7] [1]
Can I use functional medicine for cancer?
No complementary approach has been shown to cure cancer, and NCCIH advises against using unproven approaches to replace or delay treatment. [10]
More details: evidence, limits and cautions
The details behind this page: cautions, limits of the evidence and where sources disagree. Open any note to read it.
Who should check with a clinician first
References
- Drawing a line between integrative and functional medicine. Am J Med. 2026 (review by authors at Yale School of Medicine and NYU Grossman School of Medicine; abstract read). Read 2026-10-22.
- Beidelschies M, et al. Association of the Functional Medicine Model of Care With Patient-Reported Health-Related Quality-of-Life Outcomes. JAMA Netw Open. 2019 (authors at the Cleveland Clinic Center for Functional Medicine). Read 2026-10-22.
- A functional medicine approach to diabetes control and quality of life: an open-label randomized pilot study. J Clin Transl Endocrinol. 2026 (Cleveland Clinic and Case Western Reserve authors). Read 2026-10-22.
- Functional medicine health coaching improved elimination diet compliance and patient-reported health outcomes: Results from a randomized controlled trial. Medicine (Baltimore). 2024 (authors include University of Maryland and the Institute for Functional Medicine). Read 2026-10-22.
- Strobel TM, et al. Functional Medicine Approach to Patient Care Improves Sleep, Fatigue, and Quality of Life in Patients With Inflammatory Bowel Disease. Crohns Colitis 360. 2022. Read 2026-10-22.
- The Integrative Personalized Functional Medicine Approach to Reverse Cognitive Decline: Academic Experience of the First 51 Patients Case Series. 2026 (George Washington University authors; retrospective case series). Read 2026-10-22.
- Bellamy J. AAFP: Functional Medicine lacks supporting evidence; includes "harmful" and "dangerous" treatments. Science-Based Medicine, October 26, 2017 (a critical commentary; it quotes the Institute for Functional Medicine). Read 2026-10-22.
- Cleveland Clinic. Center for Functional Medicine (the clinic's own description of its service). Read 2026-10-22.
- Crawford C. AAFP Credit System Reconsiders Functional Medicine Topics. AAFP News, March 28, 2018. Read 2026-10-22.
- NCCIH. Cancer and Complementary Health Approaches: What You Need To Know. Read 2026-10-22.