Perhaps the best way would be what the Heaven's Gate cult did back in March 1997. You can Google this to find out more, including photos. But in short, 39 members of this "doomsday" cult committed mass suicide by taking phenobarbital mixed with apple sauce or pudding and washed it down with vodka with plastic bags secured over their heads. Phenobarbital should not be confused with Pentobarbital (aka: Nembutal). Phenobarbital is a much slower, longer-acting drug. Chances are it was NOT the drug that killed them, but rather the drug that caused them to go into a very deep sleep and with the plastic bags over their heads, dying of hypoxia (lack of oxygen to the brain). By being in this deep sleep, the drug effectively turned off any survival instinct such as the Hypercapnic Alarm Response that would kick in otherwise to remove the bag when the build-up of CO2 in the bag (and blood) got too high. This allowed everyone to die peacefully and painlessly in their sleep, likely never being aware that they were dying. Much like being under general anesthesia for surgery. In fact, it was reported that the police who were first on the scene said everyone looked to be sleeping. In other words, no signs of panic or fear, or contorted facial expressions, or anything like that. Just a sense of slumber. The evidence seems to suggest it was both peaceful and reliable. A 100% success rate as all 39 died, regardless of age, gender (18 men, 21 women), weight, and overall health condition. The ages ranged between 26 and 72.