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You can drink the same beer, wine, or cocktail for years, then one day a small amount makes you feel awful. Maybe your face turns red, your stomach cramps, your nose stuffs up, or you break out in hives. That sudden shift is often called “sudden alcohol intolerance,” and it can feel confusing and scary.

Some people describe these reactions as an “alcohol allergy.” True allergy to ethanol is uncommon, but allergy-type reactions can happen when the trigger is an ingredient in the drink. Either way, new symptoms after drinking deserve attention, because a few causes can be dangerous.

This guide explains what may be happening, how to tell the difference between intolerance and allergy-like reactions, and when it’s time to get medical help or addiction support.

If you or someone you love is preparing to stop drinking, you may hear the care team talk about giving “thiamine” or “vitamin B1” before or during alcohol withdrawal. It can sound like a simple vitamin fix. In reality, thiamine is a critical, brain‑protective treatment—and the fact that you need it is a strong sign that alcohol detox should never happen alone.

This guide explains why doctors rely on thiamine for alcohol withdrawal, what thiamine can and cannot do, and how to get safe, medically supervised help instead of trying to detox at home.