Why does the US use a complex 3 injection cocktail? In countries where assisted suicide is legal people just swallow a pill and go peacefully to sleep. Yet in the US there is this "crisis" of not being abel to source the injections needed. Pets are also put down very easily with a single injection which makes them go to sleep and the heart beats slower and slower until it stops in a few minutes.
Many medical doctors (persons with legal authority to prescribe drugs) and pharmacists (persons with legal authority to dispense drugs) object to capital punishment, and thus will not supply prisons with drugs that have the sole purpose of killing someone.