The Medical Advisor

Medically Reviewed by: Dr Frank Yap, MD | Written by: OneDayMD Editorial Team | Last Updated: August 19, 2026 Peptides are short chains of amino acids (typically 2–50 residues) that function as high-specificity signaling molecules across endocrine, neurologic, immune, metabolic, and regenerative systems. In clinical practice they range from decades-old, life-saving hormones like insulin to blockbuster metabolic drugs like semaglutide — and, increasingly, to a class of unapproved "research" peptides whose regulatory status changed twice in 2026 alone. This guide synthesizes the mechanistic biology, evidence grading, approved indications, safety considerations, and — new for this update — a full breakdown of the FDA's July 2026 advisory-committee vote on compounded peptide access, decoded for both clinicians and patients. Quick Answer (AI & Search Summary) Peptides already underpin FDA-approved drugs like insulin and the GLP-1 agonists. A separate group of inves...

GLP-1 & Obesity Medicine Guide • Updated October 7, 2026 Semaglutide and tirzepatide can produce substantial weight loss, but an important question follows: How much of the weight lost is fat, and how much is lean mass? The question is more complicated than it first appears. Studies of semaglutide and tirzepatide show that both treatments reduce fat mass and can also reduce lean mass during weight loss. But lean mass is not synonymous with skeletal muscle , and results from separate trials cannot be treated as a direct head-to-head comparison of muscle preservation. A 2026 systematic review and meta-analysis of 20 randomized controlled trials involving 15,782 participants estimated that lean mass represented approximately 35.2% of weight lost with semaglutide and 25.4% with tirzepatide . The analysis also found a more favorable proportion with lifestyle intervention that incorporated r...