It is commonly thought alcohol in the evening or before bed can cause relaxation and initiate sleep. However, more scientific information shows the sleep you get from alcohol is lighter and more disrupted, leaving you with less restorative sleep.
Alcohol stimulates GABA receptors in the brain. GABA is a major inhibitory neurotransmitter which causes a calming or slowing down of excitation. This stimulation increases the levels of GABA into the neurons. However, when GABA is metabolized, it can turn into Glutamate, which is a major excitatory neurotransmitter which then can cause arousal and lighter sleep. This maybe one reason why many people wind up waking up in the middle of the night after having a cocktail.
If you suffer from sleep issues, be careful not to use alcohol to help you fall asleep. The overall sleep quality is adversely affected and not worth it.