I believe the phenobarbital cocktail can take as much as three days to kill

I'd have to double-check though.
Ive been reading about it tho. There are cases of death due to pheno&alcohol. But can add more things not just those 2.
it says :
The National Institutes of Health (NIH) reports that overdosing on barbiturates like phenobarbital, either alone or combined with alcohol, results in death for about 1 in 10 people.
also here
Combination of phenobarbital and alcohol that at least some members of Heaven's Gate cult apparently took to commit suicide in Rancho Santa Fe, Calif, is well known as lethal mixture (S)
www.nytimes.com
The combination of phenobarbital and alcohol that at least some members of a cult apparently took to commit suicide in Rancho Santa Fe, Calif., is well known to be a lethal mixture.
Phenobarbital generally goes to work 10 minutes to an hour after ingestion; the interval depends in part on the amount of food in the stomach. The drug causes drowsiness, and in large amounts produces coma. Because it also depresses the mechanisms that drive the body to breathe automatically, respirations become shallow and usually fewer.
The combination of phenobarbital and alcohol reduces blood pressure and depresses the brain's centers that help make the heart beat regularly. With a large enough dose, circulation fails. The result is death.
The combination is often used in suicide. The radical protester Abbie Hoffman, for example, killed himself in 1989 by taking about 150 phenobarbital pills and washing them down with alcohol.