Two drinks containing the same amount of alcohol do not produce the same next morning. The difference comes from congeners, the minor compounds produced alongside ethanol during fermentation and ageing.
Congeners are everything that is not ethanol
Fermentation produces a range of alcohols, esters and aldehydes besides ethanol, and these carry most of what a drink tastes and smells like.
They are the reason a spirit made from grain differs from one made from agave. Removing them entirely would remove the character along with them.
The body processes several of these compounds more slowly than ethanol, and some break down into substances that are more reactive than their parent.
Distillation and ageing move the total in opposite directions
Distillation separates compounds by boiling point, and the distiller discards the earliest and latest fractions where the harshest congeners concentrate.
A spirit distilled to a high strength and filtered carries very few. This is why clear, heavily rectified spirits sit at the low end of the range.
Barrel ageing then adds compounds back, drawing them from the wood over years, which is why dark spirits carry substantially more than clear ones.
The gap between categories is large
Measured congener content differs by more than an order of magnitude between the lightest and heaviest common drink types.
Heavily aged dark spirits and some traditionally made wines sit at the top. Highly rectified clear spirits sit at the bottom.
That range is wide enough to be noticeable at the same alcohol intake, which matches what most drinkers report from experience.
Dehydration and sleep disruption run in parallel
Alcohol suppresses the hormone that limits urine production, so fluid loss exceeds fluid taken in regardless of which drink was chosen.
It also fragments sleep in the second half of the night, reducing restorative sleep even when total hours look normal.
These effects track total alcohol rather than congener content, which is why the amount consumed remains the dominant variable by a wide margin.
Why the drink type is the smaller factor
Congeners explain differences between equal quantities, not differences between quantities.
A large amount of a low-congener drink produces a worse outcome than a small amount of a high-congener one, and no choice of category changes that ordering.
Treating the drink type as the deciding factor inverts the actual weighting, which is the most common misreading of the congener research.