Temporary effects you might notice while drinking alcohol (or shortly after) can include:
feelings of relaxation or drowsiness
a sense of euphoria or giddiness
changes in mood
lowered inhibitions
impulsive behavior
slowed or slurred speech
nausea and vomiting
diarrhea
head pain
changes in hearing, vision, and perception
loss of coordination
trouble focusing or making decisions
loss of consciousness or gaps in memory (often called a blackout)
Some of these effects, like a relaxed mood or lowered inhibitions, might show up quickly after just one drink. Others, like loss of consciousness or slurred speech, may develop after a few drinks.
Dehydration-related effects, like nausea, headache, and dizziness, might not appear for a few hours, and they can also depend on what you drink, how much you drink, and if you also drink water.
These effects might not last very long, but that doesn’t make them insignificant. Impulsiveness, loss of coordination, and changes in mood can affect your judgment and behavior and contribute to more far-reaching effects, including accidents, injuries, and decisions you later regret.