Glossary
Stack
Also written stacking, combination, running together
Several separate compounds run at the same time, each in its own vial and on its own schedule.
The word this site is built on and the one it never defined. A stack is a plan: two or more compounds taken over the same period, each drawn from its own vial, each with its own dose, frequency and route.
The distinction that matters is against a blend. A blend is one vial holding several peptides at a ratio somebody else chose, so dosing one of them doses all of them. A stack keeps them apart, which keeps the schedule and the dose of each under your control — and costs more vials, more injections and more to buy.
Nothing about combining compounds is supported by evidence in the way a single compound can be. Almost no combination has been studied as a combination, so a stack is an argument from each part rather than a finding about the whole.