Hi, this is Dr. Yoon Hang Kim. I’m an integrative and functional medicine physician with expertise in low-dose naltrexone, or LDN, and in treating mast cell activation syndrome, or MCAS. Today, I want to talk about the diagnosis of MCAS. I recently shared the chapter about MCAS, and one of the comments was, “Why bother? There’s no good way to diagnose it.” I understand that frustration. The diagnostic criteria for MCAS are clear, but testing can be challenging. Histamine is processed by the body quickly. When measuring blood markers such as histamine or tryptase, timing in relation to a symptom episode matters. Testing may not capture what’s happening if that window is missed. There are also urine tests that measure breakdown products of mast cell mediators, including tests that involve a 24-hour urine collection. But cost and access can be barriers. I believe we need testing that is more accurate, affordable, and accessible. This is where I think the science and art of medicine meet. A careful history can raise suspicion for MCAS, even when previous testing has been unrevealing. That clinical suspicion is not the same as a confirmed diagnosis, but it can help guide how we evaluate and care for someone. By the time many patients come to me, they’ve already seen allergists and sometimes integrative or functional medicine physicians. I don’t want to automatically start a new workup when the likelihood of finding something new appears low. In those situations, I often focus on treating symptoms clinically. But that approach requires a good understanding of MCAS, its clinical patterns, and the limitations of testing. I’ve cared for patients with MCAS for many years, including well before COVID. MCAS received more attention after COVID, but it certainly existed before then. Before COVID, I might see a patient with MCAS once a year. Now, patients with MCAS make up more than half of my practice. Thank you for watching. This is Dr. Kim. Follow me to learn more.

To tell whether low-dose naltrexone (LDN) is having an effect, first define the condition you are treating and the specific outcome you hope to improve, such as pain, fatigue, sleep, or another symptom. Then take LDN and observe whether that outcome changes over time. Pay attention to how large the change is, whether a higher or lower dose changes the effect, and whether the response makes biological and clinical sense. Looking at these factors can help you judge whether the improvement is likely related to LDN rather than normal day-to-day changes or other influences.

Most people with MCAS don't get better from one medication. They get better from a sequence. I just finished a clinical chapter laying out the layered model I use — and one thing I did differently: I graded the evidence honestly instead of presenting everything as equally proven. The foundation isn't a drug at all. It's trigger identification, and an anaphylaxis action plan for anyone at risk. From there: antihistamines, then mast cell stabilizers, then the conventional escalation agents most integrative articles skip entirely. LDN sits in the layer above that — as an addition to a foundation, not a replacement for it. I went back through what we actually have on LDN in MCAS. It's case reports and small uncontrolled series. I cut a widely-circulated statistic from my own draft because I couldn't trace it to a citable source. The mechanism is plausible. The evidence is early. Both things are true, and you deserve to hear them together. Free to read — link in comments. Yoon Hang Kim, MD, MPH | Board-Certified in Preventive Medicine | Integrative & Functional Medicine Physician

📍 The patients I could not help immediately have often taught me the most. When I encounter a patient with a complex condition—and the usual approaches are not enough—it does not make me want to give up. It puts me into overdrive. I begin studying, asking questions, and searching for every reasonable option that might help. In Korea, the legendary physician Heo Jun emphasized that genuine compassion for a patient’s suffering is essential to healing. That principle has stayed with me throughout my career. In fact, I first learned about low-dose naltrexone because of a patient. More recently, through my online education and advocacy work, someone asked me: “Have you heard of amlexanox?” That question led me to begin researching another potential treatment option—one I might not have encountered without listening to the patient community. For people with complicated health concerns, healing is often a team effort. The physician brings medical knowledge and clinical judgment, while patients bring their lived experience, observations, and sometimes even the question that opens a new door. The best medicine can begin with humility: “I may not know the answer yet, but I am willing to keep learning.” Have you ever introduced your physician to a treatment or idea that ultimately helped you? —Yoon Hang Kim, MD Integrative & Functional Medicine Physician Follow me for more discussions about complex conditions, emerging treatment options, and individualized care. #IntegrativeMedicine #FunctionalMedicine #PatientCenteredCare #ComplexChronicIllness #LowDoseNaltrexone #LDN #MedicalEducation #NeverStopLearning

Can just 1 microgram of LDN improve sleep? For one highly sensitive patient, that tiny dose appeared to make a remarkable difference. Hi, this is Dr. Yoon Hang Kim. I’m an integrative and functional medicine physician and an expert in low-dose naltrexone. LDN may help some people fall asleep more easily, experience fewer nighttime interruptions, and wake feeling more restored. However, the right dose can vary dramatically from person to person. Many patients begin LDN somewhere between 0.5 and 1.5 mg. More sensitive patients may start at 0.1 mg or lower. In this case, I had reason to believe that even those doses might be too high, so we started at just 1 microgram—one-thousandth of a milligram. The result was remarkable. The patient, who had struggled with sleep for a long time, began falling asleep more easily, waking less often, and experiencing more restorative sleep. Their sleep cycle appears to be returning toward baseline. This case highlights an important principle: with LDN, the lowest effective dose may be far lower than the standard starting dose. Sometimes the key is not simply choosing the right medication. It is discerning the right dose for that individual. Please follow me to learn more about personalized LDN therapy.