The reason athletes have become interested in peptides is that they serve as signaling molecules. Instead of taking, say, human growth hormone, you can take a peptide that tells your body to The Human Lab Rats Injecting Themselves with Peptides Office for Science and Society McGill University IGF 1 LR3: Nasal Spray vs. Subcutaneous Injection Comparison An FDA Reversal on Peptides Could Open the Market to Unsafe Drugs ProPublica