Functional Medicine Doctor in New York City, NY

Medically reviewed by Dr. David Borenstein, MD. Last reviewed November 2026.

In short: Dr. David Borenstein is a New York physician and functional medicine practitioner who has practiced in Manhattan for over 20 years. He looks for the root cause of chronic symptoms such as fatigue, thyroid problems, gut issues and hormone imbalance, using detailed history, advanced lab testing and a personalized treatment plan. His office is at 308 Fifth Avenue in Midtown Manhattan, with telemedicine available.

You’ve seen your primary care doctor. Maybe an endocrinologist, a gastroenterologist and a rheumatologist, too. Each one ran tests, told you the results were “normal,” and sent you home still exhausted, bloated, foggy or in pain.

That gap between “normal labs” and how you actually feel is where functional medicine starts.

Functional medicine is a physician-led approach that identifies and treats the underlying causes of chronic illness, rather than only managing symptoms. It treats the body as connected systems: gut, hormones, immune function, metabolism and stress response all affect each other.

Dr. Borenstein likes to quote the Institute for Functional Medicine’s principle: one condition can have many causes, and one cause can produce many conditions. Your fatigue may come from your thyroid, your gut, your sleep, or all three. His job is to find out which.

Call Manhattan Integrative Medicine at (212) 262-2412 or request a consultation.

In short: Dr. David Borenstein is a New York physician and functional medicine practitioner who has practiced in Manhattan for over 20 years. He looks for the root cause of chronic symptoms such as fatigue, thyroid problems, gut issues and hormone imbalance, using detailed history, advanced lab testing and a personalized treatment plan. His office is at 308 Fifth Avenue in Midtown Manhattan, with telemedicine available.

You’ve seen your primary care doctor. Maybe an endocrinologist, a gastroenterologist and a rheumatologist, too. Each one ran tests, told you the results were “normal,” and sent you home still exhausted, bloated, foggy or in pain.

That gap between “normal labs” and how you actually feel is where functional medicine starts.

Functional medicine is a physician-led approach that identifies and treats the underlying causes of chronic illness, rather than only managing symptoms. It treats the body as connected systems: gut, hormones, immune function, metabolism and stress response all affect each other.

Dr. Borenstein likes to quote the Institute for Functional Medicine’s principle: one condition can have many causes, and one cause can produce many conditions. Your fatigue may come from your thyroid, your gut, your sleep, or all three. His job is to find out which.

Call Manhattan Integrative Medicine at (212) 262-2412 or request a consultation.

What does a functional medicine doctor do?

A functional medicine doctor is a licensed physician who spends more time on each patient, orders broader testing, and connects findings across body systems that conventional care usually treats separately.

Functional medicine does not replace conventional medicine. Dr. Borenstein is a board-certified physician who prescribes medication, orders imaging, and refers to specialists when that is the right call.

Who sees a functional medicine doctor?

Most of Dr. Borenstein’s patients come with one of these patterns:

• Fatigue that rest doesn’t fix, often diagnosed as chronic fatigue syndrome
• Widespread pain and poor sleep from fibromyalgia
• Hypothyroid symptoms with “normal” TSH, or Hashimoto’s
• Bloating, gas and irregular bowels from SIBO or leaky gut
• Menopause, andropause or low testosterone
• Weight gain that diet and exercise don’t move
• Mold exposure, which is common in older, water-damaged New York buildings
• Lingering symptoms after COVID-19 (long COVID)
• Prediabetes or type 2 diabetes
• Healthy adults who want a proactive plan for longevity and healthy aging

What happens at your first visit

1. History. Dr. Borenstein reviews your symptoms, timeline, prior labs, medications, diet, sleep, stress and environment. Bring every lab report you have.
2. Exam. A full physical exam.
3. Testing. He orders the labs your history points to (see below). Specialty tests such as Genova Diagnostics panels may be included.
4. Results visit. He explains what each result means and how the findings connect.
5. Your plan. A written, prioritized plan: what to treat first, what to change, and when to re-test.

Tests a functional medicine doctor may order

Not every patient needs every test. Dr. Borenstein orders what your history justifies.

Treatments Dr. Borenstein uses

• Hormone therapy: bioidentical hormone replacement for women and men, and thyroid treatment including T3/T4 combinations
• Low dose naltrexone (LDN) for autoimmune and inflammatory conditions
• Gut protocols: targeted antibiotics or herbal antimicrobials, prokinetics, and diet changes
• Nutrition and supplements matched to measured deficiencies
• Sleep and stress protocols, including the S.H.I.N.E.® approach he uses for fibromyalgia and CFS
• Metabolic weight loss through the Manhattan Metabolism program
• Prescription medication whenever it is the right tool

Results vary by age, genetics, overall health and how closely the plan is followed.

About Dr. David Borenstein, MD

Dr. Borenstein earned his medical degree at the Technion Faculty of Medicine in Israel and completed his internship at Staten Island University Hospital. He is board-certified in Physical Medicine and Rehabilitation, certified in Medical Acupuncture, and a member of the Institute for Functional Medicine, ACAM and A4M. He has been quoted on thyroid and hormone health by Vogue, Everyday Health and the Chicago Tribune.

Visiting our Manhattan office

Manhattan Integrative Medicine, 308 Fifth Avenue, 5th Floor, New York, NY 10001, near Herald Square and the Empire State Building. Monday–Thursday 8am–5pm, Friday 9am–5pm. Telemedicine is available. We also see patients on Fridays in Huntington, Long Island.

Frequently asked questions

What is the difference between functional and integrative medicine?

Functional medicine is a method: finding and treating root causes across connected body systems. Integrative medicine is a philosophy of combining conventional and complementary treatments. Dr. Borenstein practices both: he uses the functional method to diagnose and draws on conventional and complementary tools to treat.

Is a functional medicine practitioner a real doctor?

Titles vary. Some functional medicine practitioners are chiropractors, nutritionists or health coaches. Dr. Borenstein is a licensed medical doctor (MD) in New York, board-certified in Physical Medicine and Rehabilitation, who can order any lab test and prescribe medication.

Does insurance cover functional medicine in NYC?

Manhattan Integrative Medicine does not accept private insurance, Medicare or Medicaid. Visits are self-pay.

How long until I feel better?

It depends on the cause. Thyroid and hormone corrections often show change within 6–12 weeks; gut and chronic fatigue cases can take several months. Dr. Borenstein re-tests and adjusts along the way.

What conditions does functional medicine treat?

At this practice: chronic fatigue, fibromyalgia, thyroid disorders and Hashimoto’s, SIBO and digestive issues, hormone imbalance, menopause, low testosterone, weight gain, insulin resistance, mold exposure and long COVID.

Can I see Dr. Borenstein by telemedicine?

Yes. Follow-ups and many initial visits can be done by video. Some patients need an in-person exam first.

Do I need a referral?

No. Call (212) 262-2412 or request a consultation online.

Reserve your appointment

If you’ve been told your labs are normal but you don’t feel normal, a root-cause evaluation is the next step. Call Dr. Borenstein at (212) 262-2412 or contact us here.

Serving patients across New York City: Manhattan (Midtown, NoMad, Flatiron, Chelsea, Murray Hill, Gramercy, the Upper East Side and the Upper West Side), Brooklyn, Queens, the Bronx and Staten Island, plus Long Island, Westchester and the greater New York metro area.