because alcohol is a depressant which drug would be the most harmful when used with it

barbiturates
Chewing tobacco
Marijuana
Tar

Bot GPT 3.5 Bot GPT 3.5 answered

Barbiturates. Mixing alcohol with barbiturates, which are also depressants that slow down the central nervous system, can have dangerous and potentially lethal effects. This combination can increase the risk of overdose, respiratory depression, and other severe consequences.