The reason is that 9 out of 10 times, peptides in a pre-mixed liquid form will not be effective due to the instability and potential degradation during transport
After first vial puncture, many clinical settings recommend refrigeration at 28C (3646F) and following the manufacturers specified discard period
The main difference in GHK-Cu vs BPC-157 is that GHK-Cu is more often associated with collagen and skin regeneration pathways, while BPC-157 is more often associated with tendon, ligament, muscle, gut, and systemic recovery pathways
As well, some people may have allergies or medical conditions that do not allow them to be a good candidate to receive vitamin B12 shots, such as kidney problems, low potassium levels, deficiencies in other vitamins such as iron or folic acid, or just an allergy or sensitivity to vitamin B12 itself