What is intestinal methane overgrowth?

Intestinal Methane Overgrowth (IMO) is the clinical term for methane-dominant SIBO, diagnosed when a breath test detects methane levels of 10 ppm or higher at any point. Unlike standard SIBO, which is caused by bacteria, IMO is driven by methanogenic archaea—primarily Methanobrevibacter smithii. Archaea are single-celled organisms that consume the hydrogen gas produced by neighboring bacteria and convert it into methane gas. Furthermore, because archaea can thrive in both the small and large intestines, the condition is not restricted solely to the small bowel. The primary symptom of IMO is chronic, treatment-resistant constipation, as methane gas acts as a neuromuscular inhibitor that slows digestive transit. To learn how to treat this specific overgrowth, read our guide on [methane SIBO](/methane-sibo).

Disclaimer: This content is reviewed and fact-checked by Daryl Stubbs, Certified Holistic Nutritional Consultant (C.H.N.C), for educational purposes. It does not constitute medical advice or a doctor-patient relationship.