Why alpha-2 receptors make some fat slow to mobilize
Fat cells carry two opposing adrenergic receptor types. Beta receptors, when stimulated by catecholamines, promote fat breakdown, while alpha-2 receptors act as a brake that suppresses it. Lower-body and gluteofemoral depots, often described as stubborn fat, tend to be relatively dense in alpha-2 receptors, so catecholamines mobilize them more slowly than abdominal fat.
Yohimbine is an alpha-2 antagonist. By blocking that brake, it can in principle allow catecholamine-driven lipolysis to proceed more freely in those depots, which is the rationale behind its use during fasted training.
Limits, variability, and safety
Human evidence is mixed and effects are modest at best; insulin blunts yohimbine's action, so it is generally taken fasted. Individual response varies widely with genetics and dose.
This is general educational information, not medical advice. Yohimbine can raise heart rate and blood pressure and trigger anxiety, and it interacts with several medications. It is unsuitable for people with cardiovascular conditions or anxiety disorders, and a clinician should be consulted before use.