I can only comment on what was done in the state of Oregon, where they have assisted death. There the patient is given two euthanasia kits in case one of the kits is found to be defective. The kit is an inclusive kit that contains two different medications. One is designed to prevent vomiting, and the second one is the barbiturate, which brings upon death. That's my understanding of what is used there.
On May 2nd, 2016. See this statement in context.