Most peptide harm does not come from the pharmacology. It comes from contamination, wrong concentrations, unsterile technique, and interactions nobody checked — all of which are avoidable, and none of which depend on whether the compound works.
Product quality is the first problem. Compounds sold for research use are not manufactured to pharmaceutical standards and are not inspected as though they were. Independent assay data on this site shows measured purity varying between vendors and between lots of the same vendor. A certificate of analysis covers the lot that was submitted and nothing else, and purity is not identity: a sample can assay clean and still be the wrong compound or the wrong strength.
Dose arithmetic is the second. Reconstitution converts a mass into a concentration, and the conversion into insulin-syringe units is where errors concentrate. An order-of-magnitude slip there is far more dangerous than the compound itself in most cases.
Interactions are the third, and the most commonly skipped. Several peptide classes have real interaction profiles — GLP-1 agonists slow gastric emptying and change the absorption of oral medication, and growth hormone secretagogues affect glucose handling. Individual compound profiles list documented interactions and contraindications where they exist.
Injection practice matters independently of everything above: sterile technique, single-use needles, correct storage of reconstituted product, and safe sharps disposal. Reconstituted peptides are usually refrigerated and have a limited usable window that varies by compound.
Nothing on this site is medical advice, and peptides described as "research use only" are not approved for human consumption. If you are considering any of this, a clinician who knows your history is a better source than any website — including this one.
Related: Peptide library, Vendor directory, Independent lab tests, How we rate vendors.