Treatment Database

A mast cell stabilizer that reduces the release of histamine and other mediators from activated mast cells. Oral cromolyn is FDA-approved for mastocytosis on the basis of four small randomized controlled trials (32 evaluable patients), and it is a standard treatment for mast cell activation syndrome (MCAS). Less than 1% of an oral dose is absorbed, so it acts mainly in the gut, though patients often report benefits elsewhere. The label dose for adults is 200 mg four times daily (800 mg/day), taken 30 minutes before meals and at bedtime; it may be increased if there is no response after 2–3 weeks, up to 40 mg/kg/day, and improvement typically appears within 2–6 weeks. A 2026 Johns Hopkins case series (Christoforou, Rowe et al., Cureus) described five people with ME/CFS and MCAS, two of whom also had Long COVID, who had not responded fully to 800 mg/day. They dissolved the whole day's dose in an opaque bottle of non-alkaline water and sipped it throughout the day, raising the dose weekly to 1600–2400 mg/day. All five improved, including flushing, hives, GI symptoms, lightheadedness, fatigue and PEM; wellness scores rose from 20–60 to 61–86 out of 100, with no side effects reported over 12–42 months. Two patients worsened during a cromolyn shortage. The series was not consecutive and had no control group, so the authors call for randomized trials. In the TREATME patient survey, 36% of people with Long COVID who tried oral cromolyn (n=33) reported moderate to much better improvement, compared with 10.5% for intranasal cromolyn (n=38). Cromolyn is also available as a nasal spray, eye drops and inhaler for local symptoms.