It is a popular modality for use by health care providers whose practice is largely within conventional medicine. 
Functional medicine focuses on interactions between the environment and the gastrointestinal, endocrine, and immune systems of patients. Practitioners attempt to develop individual treatment plans for each patient.
Functional medicine typically seeks to provide chronic care management based on the assumption that "diet, nutrition, and exposure to environmental toxins play central roles in a predisposition to illness and "provoke symptoms, and modulate the activity of biochemical mediators through a complex and diverse set of mechanisms."
Functional medicine was developed and originated by Dr. Helmut W. Schimmel.
Systems biology approach
Functional medicine reflects a systems biology approach which involves an analysis of how all components of the human biological system interact functionally with the environment over time. The Institute for Functional Medicine contrasts this approach with an organ system biology broken down into modern medical specialties.
Functional medicine, in agreement with modern medicine, holds that the entire "patient story" needs to be heard and understood in context in order to truly help the patient. Where functional medicine differs from mainstream medicine is its willingness to employ treatments and drugs which may not be well evidenced by clinical research,  including orthomolecular medicine  and detoxification of unevidenced toxins.
The Institute for Functional Medicine
Jeffrey Bland, PhD, and Susan Bland founded the Institute for Functional Medicine (IFM) in 1993. IFM is a nonprofit educational organization that provides continuing medical education for health care providers. The Institute for Functional Medicine is accredited by the Accreditation Council for Continuing Medical Education and achieved its accreditation from the Accreditation Council for Continuing Medical Education on September 12, 2006 and was awarded the status of Accreditation with Commendation for six years as a provider of continuing medical education for physicians.
In 1991, the U.S. Federal Trade Commission charged that two corporations led by Jeffrey Bland, HealthComm and Nu-Day Enterprises, had falsely claimed that their diet program could cause weight loss by changing consumers' metabolism and cause them to lose weight without exercising so that fat would be lost as body heat instead of being stored. In 1995, the FTC charged Bland and his companies with violating the 1991 consent order by making further unsubstantiated weight-loss claims for several products, including the UltraClear dietary program, which had been falsely claimed to reduce the incidence and severity of symptoms associated with gastrointestinal problems, inflammatory and immunologic problems, fatigue, food allergies, mercury exposure, kidney disorders, and rheumatoid arthritis. The second settlement agreement included a $45,000 civil penalty.
- Pal, Sanjoy (2002). "Complementary and alternative medicine: An overview". Current Science.
- Ehrlich, Gillian; Travis Callender, Barak Gaster (May 2013). "Integrative Medicine at Academic Health Centers: A Survey of Clinicians’ Educational Backgrounds and Practices". Family Medicine 45 (5): 330–334. Retrieved 8 October 2013.
- Galland L (2006). "Patient-centered care: antecedents, triggers, and mediators". Alternative Therapies in Health and Medicine 12 (4): 62–70. PMID 16862744.
- Schimmel, Functional Medicine- The Origin and Treatment of Chronic Diseases, Karl F. Haug Verlag; Germany 1996. ISBN 3-7760-1635-3
- Jones DS, ed. Textbook of Functional Medicine. Gig Harbor, WA: The Institute for Functional Medicine; 2005. ISBN 0977371301[page needed]
- Jones DS. Functional medicine model: Comprehensive care for complex, chronic disease. http://www.functionalmedicine.org/eduprog/webinar_series.asp
- Sampson W. Functional Medicine- New Kid on the Block. http://www.sciencebasedmedicine.org/?p=271
- Center for Functional Medicine - Nutritional Medicine/Orthomolecular Medicine. http://www.centerforfunctionalmed.com/nutritional_medicine_orthomolecular_medicine.htm
- Center for Functional Medicine - Detoxification/ Heavy Metals. http://www.centerforfunctionalmed.com/detoxification_heavy_metals.htm
- FTC charges diet company's "infomercials" contained false and unsubstantiated claims about its diet program; Consent agreement settles charges. FTC News Release, Oct 30, 1991.
- Defendants in a previous FTC lawsuit agree to pay $45,000 civil penalty to settle charges. FTC News Release, Jan 19, 1995.
- Stephen Barrett, M.D., Some Notes on Jeffrey Bland, Quackwatch