Positives

• Ostarine may be of interest to some chronic illness patients because muscle loss, weakness, and deconditioning can follow prolonged Long COVID or ME/CFS disability (Wikipedia).
• Its relevance is theoretical and mostly about body composition, not the core post-viral mechanisms that drive PEM, brain fog, dysautonomia, or MCAS symptoms (WebMD).

Negatives

• There is no established evidence that ostarine improves Long COVID, ME/CFS, Lyme, POTS, MCAS, or chronic fatigue (WebMD).
• Improving lean mass does not necessarily improve functional capacity if exertion still triggers symptom crashes (US Pharmacist).

Hurdles & Side Effects

• Ostarine is an unapproved SARM, and quality control is a major issue with research-chemical products (US Pharmacist).
• Potential concerns include liver injury, hormone suppression, lipid changes, mood changes, acne, hair loss, and cardiovascular risk (WebMD).