While many shelters practice humane euthanasia by injection of approved drugs, some still use the gas chamber. (animalaidusa.org)
When it is given by injection in humans, it is used to control high blood pressure. (2ndchance.info)
By comparison, the use of euthanasia by injection causes animals to lose consciousness and brain function before their vital organs shut down, decreasing suffering and resulting in rapid clinical death. (animallawcoalition.com)