San Antonio TX Integrative Functional Medicine - Yoon Hang Kim MD

San Antonio TX Integrative Functional Medicine - Yoon Hang Kim MD Dr. Kim provides integrative medicine, functional medicine and LDN therapy online in IA, IL, MO, GA, FL and TX

08/21/2026

Hi, this is Yoon Hang Kim, MD. I’m an integrative and functional medicine physician, board-certified in preventive medicine, with expertise in low-dose naltrexone—LDN—and a growing clinical focus on mast cell activation syndrome, or MCAS.

Today, I want to talk about the philosophy of diagnosing MCAS.

MCAS is a syndrome, and syndromes often require both established diagnostic criteria and thoughtful clinical judgment. Laboratory testing can be very helpful, but a single laboratory result rarely tells the entire story.

For example, I recently saw a patient with an elevated IgA level and a normal tryptase. Does either result prove or rule out MCAS?

The answer is no.

An elevated IgA is nonspecific and may prompt us to look more closely at the patient's immune, gastrointestinal, infectious, inflammatory, or other clinical context. It is not, by itself, diagnostic of MCAS or food allergy.

Tryptase is different. An appropriately timed rise in tryptase during a suspected mast-cell activation episode can provide strong evidence supporting mast-cell activation. However, a normal baseline tryptase does not, by itself, exclude MCAS.

I sometimes explain it with this analogy:

Suppose you tell me you saw an elk in your backyard in Texas. I might be skeptical because elk aren't commonly seen in most Texas backyards.

Now imagine you have ten photographs of your backyard, and nine show no elk. Those nine photographs do not prove that an elk was never there.

But if one clear photograph shows the elk standing in your backyard, that's meaningful evidence.

MCAS testing can sometimes feel similar. A negative test obtained at the wrong time may not settle the question, while an appropriately obtained positive finding can be very informative.

That is why MCAS should be evaluated by putting the entire picture together: symptoms, timing, objective evidence of mast-cell mediator release when obtainable, response to appropriate treatment, and consideration of alternative diagnoses.

This is Yoon Hang Kim, MD. Follow me to learn more about integrative medicine, functional medicine, LDN, and MCAS.

08/21/2026

Someone recently asked me how my public health and preventive medicine background connects to what I do now as an integrative medicine physician.
Short answer? It changed everything.
I started in family medicine. I had about four and a half years of outpatient medicine and two and a half years of inpatient work under my belt. But family medicine, the way it was structured, felt more like being a medical social worker than a physician. The dean of my medical school actually warned me — she knew I'd received the Howard Hughes Research Fellowship, and she told me I'd probably get bored. She was right.
But the public health training? That gave me something different. It gave me a lens for expanding access. For ten years, I built integrative medicine programs inside large health systems. I created programs that served Medicare patients, Medicare Advantage patients, even Medicaid patients in Illinois. Every single organization I consulted for is still alive. One company that considered hiring me but didn't? They went under. I'm not saying it was me — but I'd like to think I helped.
Here's what ten years also taught me: the insurance-based system condemns integrative programs to fail. You can't create a healing space in five-minute visits. You can't do meaningful medicine while double-booking. The system is rigged against physicians, burns us out, and treats us like replaceable parts.
So now? Cash-based practice only. Some people will say that's not fair. But until the rules change, I have zero motivation to play a game that's rigged against doctors and — ultimately — against patients who deserve more than assembly-line medicine.
Did the public health background hurt me? For ten years, honestly, yes. I spent a decade fighting a system that didn't want to be fixed. But I wouldn't take it back. Not for a second. I learned too much. I helped too many people.
As I get older, I have less time. So I'm only working on projects that are likely to succeed — and that means direct care, on my terms, for people who want real medicine.
This is Dr. Kim. Thanks for the question. Keep them coming.

08/20/2026

Thirty years ago, my career looked like a jumble of pieces that didn't fit — two residencies, UCLA acupuncture training, a fellowship with Dr. Andrew Weil, research on a Nobel Prize–winning team.

Then twenty years of practice taught me the hard truth: insurance companies set the rules, and solving complex medical puzzles — spending real time with patients — isn't what the system rewards.

So I built something different. A membership practice intentionally capped at 99 people, so I can go deep with those who need it most — MCAS, integrative oncology, and other complex conditions. We've now reached capacity and opened a waitlist, and I've never been more certain this was the right path.

I still love what I do. And I'm grateful to God every day that He keeps sending me some of His people. 🙏

📍 Now serving clients via www.directintegrativecare.com — waitlist and guest visits available.

08/18/2026

MCAS can make eating feel like a minefield—but sometimes the right combination can make a remarkable difference.

One of my patients with mast cell activation syndrome had become extremely limited in the foods they could tolerate. We carefully introduced compounded ketotifen, an older antihistamine that also acts as a mast cell stabilizer, together with low-dose naltrexone (LDN).

The result? They were eventually able to tolerate a much wider variety of foods. 🙌

But here’s the important part: MCAS treatment is highly individualized. There is no single medication, dose, or protocol that works for everyone. For many patients, progress comes from going slowly, adjusting carefully, and figuring out what their body can tolerate—one step at a time.

After years of seeing MCAS both personally and professionally, I’ve learned that individualized care matters enormously.

Follow me for more on MCAS, low-dose naltrexone, functional medicine, and integrative medicine.



For educational purposes only. Treatment decisions should be made with a qualified healthcare professional.

08/16/2026

📍 📍 Hi, this is Dr. Yoon Hang Kim. Uh, I'm an integrative and functional medicine physician, and I'm an expert in LDN. I'm just looking at the LDN support group questions from, uh, school, and I'm trying to answer one or two questions. Uh, question is that, "Can LDN help with pulmonary fibrosis? I have an autoimmune condition, and in addition to regular treatment, I'm using LDN."

So if there's an autoimmune condition and if the pulmonary fibrosis is being, um, sh- worsened or created by a autoimmune process, I think LDN is a fair thing to try. Having said that, the pulmonary fibrosis, uh, is not an easy condition to treat. Um, and I do recommend that you work very closely with your pulmonologist, y- uh, and the doctor with the autoimmune condition.

And in... on top of that, I think having a functional medicine, um, expert can be helpful, and because there's a protocols in place that can be helpful, and it's not appropriate for me to just, uh, send those protocols out or share it with them because it's-- e- it-- everything has to be individualized. So for, even for me, um, I can say some people don't respond to LDN, but they, uh, they will respond to another, another option.

But another person that's been starting with that option will not work, and I have to come back to LDN. And now I have even an option, a third option, because third and fourth options because it's not easy. And like I said, uh, you've heard me saying that I think that our immune systems has changed after COVID interaction, and it doesn't matter you got the vaccine, you got...

it doesn't matter you got naturally, uh, exposed. W- I do believe that majority of us have been exposed and our immune system probably have interacted with COVID. This is Dr. Yoon Hang Kim. Uh, please follow me to learn more about LDN, mast cell activation, and functional medicine. Thank you.

08/15/2026

📍 **MCAS Is Not “Just Allergies” — and Treatment Has to Be Individualized**

Hi, this is Dr. Yoon Hang Kim.

I’ve worked in integrative and functional medicine and with Low Dose Naltrexone (LDN) for many years, and I’ve been developing deeper expertise in **Mast Cell Activation Syndrome (MCAS)** because so many patients are struggling with it—and it is not an easy condition to treat.

My first introduction to what we would now recognize as MCAS was actually in the 1980s, when a family member developed symptoms. At the time, we didn’t have the language we have today. We simply called it “allergies.”

Today, we understand that MCAS can be much more complicated than a traditional allergy.

That personal experience pushed me to research, learn, and explore different approaches—and it continues to shape how I care for patients today.

One of the biggest lessons I’ve learned is this:

**No two MCAS patients seem to respond exactly the same way.**

For example, I had one patient who could not tolerate ketotifen but responded extremely well to LDN.

Another patient did not tolerate LDN—but has done very well with ketotifen.

That is MCAS.

Treatment often requires a high degree of individualization. The dose of LDN may need to be carefully adjusted. The dose of ketotifen may need to be individualized. And sometimes medications that initially help may become less effective over time.

For many patients, I believe a **combination approach** may ultimately be the most effective strategy—addressing mast cell stabilization, inflammation, triggers, lifestyle, and the individual patient rather than relying on one medication alone.

The science is still evolving, and we still have a great deal to learn. But patients with MCAS deserve thoughtful, individualized care.

This is Dr. Kim.

Follow me to learn more about **integrative and functional medicine, LDN, and MCAS.**

08/15/2026

For more than 25 years as a physician, I’ve carried one prayer with me:

“Lord, please send me some of Your people. Let some of Your people receive Your miracle so that we can praise and bless Your name.”

That prayer has followed me into exam rooms, difficult cases, seasons of uncertainty, and moments when I could not see what God was doing.

In 2007, it was tested.

I found myself in Georgia without a job, with a family to support and no clear path forward. What felt like failure became the beginning of something I never could have planned.

One by one, people entered my life at exactly the right time.

Those relationships became a clinic.

That clinic became a community.

And now, that story is becoming a book.

THE WAY AND THE WORD
Thy Will Be Done — A Physician’s Journey into Integrative Medicine

This book is about faith, healing, surrender, and the search for a better way to practice medicine.

It explores the two traditions that have deeply shaped my understanding of healing: Christianity and Taoism. Christianity taught me that we are called to love, serve, and care for the whole person. Taoism taught me the wisdom of simplicity, balance, humility, and surrender.

I do not believe these traditions are the same. But both have challenged me to look beyond control, symptoms, and conventional definitions of health.

Because true healing is more than the absence of disease.

It is wholeness.

It is connection.

It is balance.

It is shalom.

Modern medicine is extraordinarily sophisticated, yet too often we treat people in fragments. We address laboratory values, symptoms, medications, and procedures while overlooking the grief, stress, relationships, habits, spiritual wounds, and life circumstances that may be shaping a person’s health.

That conviction led me toward integrative medicine and toward building a community where people come before profit and service comes before self.

Sometimes the path forward does not appear until we surrender the path we thought we were supposed to take.

Sometimes losing our way is how we discover the way God has prepared for us.

That is the story I want to tell.

If you’d like to read how it begins, type PREFACE in the comments. 🙏

— Yoon Hang “John” Kim, MD
www.yoonhangkim.com

08/14/2026

📍 Hi, this is Dr. Yoon Hang Kim.

I’m a physician specializing in integrative and functional medicine, with extensive experience using Low-Dose Naltrexone (LDN), and I’ve been developing a deeper focus on Mast Cell Activation Syndrome (MCAS).

In many ways, God introduced me to MCAS through a family member who had likely lived with it for most of their life. For nearly 20 years, I struggled to understand how to help this person. At the time, MCAS wasn’t well recognized. We didn’t have a name for what was happening—everything was simply called “allergies,” even though the symptoms were far more complex.

Over time, a combination of medications, supplements, LDN, and other approaches—including allergy desensitization with allergy drops—made a tremendous difference.

But today, particularly in the post-COVID era, I’m seeing MCAS presentations that can be much more severe.

There are times when I strongly encourage my patients to see an allergist and explore conventional medical treatment alongside the integrative approaches we’re using.

One patient described her skin as feeling like it was constantly burning. Her symptoms improved dramatically during a three-day fast, but obviously, fasting indefinitely is not a sustainable solution. She eventually tried a medication recommended for her condition and told me the effect felt “like magic.”

Another patient developed such severe reactions to food that maintaining a healthy weight became extremely difficult. Again, an allergist became an essential part of her care team.

That brings me to one of the most important lessons in integrative medicine:

**Good medicine is a team sport.**

It isn’t about choosing conventional medicine *or* integrative medicine. It isn’t about one doctor, one supplement, or one medication.

It’s about using the best available tools—and the right team—to help the individual patient.

This is Dr. Kim. Follow me to learn more about integrative medicine, LDN, MCAS, and how we can bring different approaches together to improve patient care.

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