The danger is found in drugs’ effect on GABA receptors.
Drugs like alcohol, barbiturates, and benzodiazepines all seems to affect the same target – the major inhibitory neurotransmitter GABA. Neurons containing GABA receptors are very common in the nervous system and their function is to inhibit other neurons. One such receptor that is affected by GABA is the GABAa receptor that contains chloride channels. When the receptor is excited, an influx of Cl ions takes place, increasing the negative charge on the inside – hyperpolarization – making initiation, or propagation of an action potential much more difficult. However, this GABAa receptor has not only a binding site for GABA, but two other binding sites as well. One is the sedative-hypnotic site, the other is the anxiety site. That’s why it is possible that both sedative-hypnotic drugs (alcohol and barbiturates) and antianxiety drugs (benzodiazepines) can bind to the same receptor, amplifying their effects. Sedative-hypnotic drugs (alcohol or barbiturates) have precisely this effect -making it hard for action potential to take place and, therefore, sedating the body and affecting bodily functions. Antianxiety drugs (benzodiazepines) enhance binding effects of GABA and so alcohol, or barbiturates will have an even stronger sedative effect, possibly leading to coma, or even death.
The threat of mixing drugs and alcohol is not just a myth, it is a deadly cocktail that you don’t want to be experimenting with.