Respiratory depression is caused by NE
C i.e. Strychnine Strychnine is a CNS and respiratory stimulantQ. Alcohol, barbiturates, opioidsQ, benzodiazepines, chloral hydrate, paraldehyde, mandrax (melsedine), heroin (brown sugar), general anesthetics, sedative & hypnotics are CNS depressants. (However few may initially stimulate CNS). Hallucinogens (LSD = peyote = mescaline = phencyclidine), ecstasy, khat (catha edulis), cocaine and amphetamine are CNS stimulants (psychotropics).
Opium
Barbiturate
Strychnine
Gelsemine