Osmolality describes the ratio of particles in the blood to fluid. If a person has more fluid than particles, the kidneys release more urine.

When a person drinks alcohol, the alcohol inhibits the body’s release of a hormone called vasopressin, also known as antidiuretic hormone (ADH).

Generally, the brain responds to an increase in particles over fluids by signaling the release of ADH. ADH then tells the kidneys to hold on to the liquid.

By inhibiting ADH, alcohol causes the kidneys to release more water, causing a dehydration effect. It can also cause headaches and nausea.

Sources - https://www.medicalnewstoday.com/articles/why-does-alcohol-make-you-pee#the-science

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