Research question
What solvent is used to reconstitute a lyophilised vial?
The vial contains lyophilised retatrutide and nothing else that you should treat as a ready solution. Bacteriostatic water is not in the carton. Neither is any other diluent. Which solvent a method uses, what grade it is, and how it is handled are decisions in the laboratory SOP. GetReta will not specify a volume, a concentration or a schedule.
A certificate of analysis describes the dry lot: identity, HPLC purity, mass-spec result, lot number and test date. Those lines do not become a recipe when liquid is added. If your method calls for water for injection, bacteriostatic water or another pharmacopoeial solvent, source that solvent separately and record the lot of the solvent beside the lot of the peptide. That pairing is what makes a later chromatogram interpretable.
Do not use the optional research pen, if you bought one, as a measuring device for a protocol GetReta has not written. The pen is an empty accessory. The product is the vial. Research use only.