l carnitine endurance athletes Scientifically Backed Triple Strength L-Carnitine L-Carnitine, Athletic Performance and Longevity

There are various causes, including excess melanin production

When the body is in a calorie deficit, it sometimes breaks down muscle along with fat for energy

Cell Microbiol 15 , 701708 (2013)

Enhancement of the immune response and protection induced by probiotic lactic acid bacteria against furunculosis in rainbow trout (Oncorhynchus mykiss)

So even though any professional athlete with this substance in their system would be automatically disqualified from competition, and the FDA put out advisories about the issues with compounding pharmacies making these substances (6,7), people are still getting their hands on BPC 157

Christensen J, Petrenaite V, Atterman J, et al