Alcohol (and more specifically ethanol, “drinking alcohol”) is a poison and a depressant drug. The fact that it is a poison often surprises people, but remember it can run your car and it is used in biology to kill insect specimens.
Ethanol has special effects on the adolescent brain, which shouldn’t be surprising when you consider that the adolescent brain is “under construction”. Just raise some kids into and/or through adolescence and you come to realize that it is “damaged” and “getting fixed” (the latter by about the time they are 22).
“Binge” drinking is particularly damaging and that is what most adolescent drinking is. Ethanol affects learning and memory much more significantly in adolescents than adults. Those effects are compounded with significant ethanol consumption (repeat or continued) as an adult. It also appears that changes occur in the adolescent brain with ethanol use that makes it more likely to develop “problem drinking” as an adult.
A significant difference between adolescent and adult drinkers is that for adolescents ethanol has less of a sedation effect and coordination is affected a bit differently. This diminishes the “natural” effects of ethanol to get an individual to stop drinking during one “setting”. Blood alcohol levels can get higher in an adolescent because it takes more for them to become “falling-down drunk” (a “natural” drinking stopper).
However, ethanol still poisons the eyes in both adolescents and adults. Initially ethanol impairs papillary constriction, so bright lights appear brighter and harder to at (think headlights). Then gaze becomes disconjugate giving you double vision. Both of these things make driving very dangerous. At the same time, ethanol makes you “stupid”. You may choose to “follow” the taillights of a parked car. You lose inhibitions, increasing the likelihood of risk taking and making “bad” choices.
This stuff can lead to your death or the death of others. A developing adolescent brain bathed in ethanol is a recipe for death and disaster.