Alcohol Absorption: Stomach vs. Small Intestine

~20% of alcohol is absorbed in the stomach (via simple diffusion across gastric mucosa); ~80% in the small intestine (duodenum/jejunum), where vast surface area (villi/microvilli) and rich blood flow enable rapid uptake.

Factors Affecting Absorption Rate

• Gastric emptying: Rate-limiting step. Food (especially fat/protein) ↓ emptying → ↓ peak BAC, delayed Tmax. Carbonation ↑ emptying.
• Concentration: 10–30% ABV fastest; very high (>40%) irritates pylorus → delayed.
• Sex: Women have lower gastric ADH (first-pass metabolism) → higher BAC per drink.
• Genetics: ADH1B*2, ALDH2*2 variants (East Asian populations) → rapid acetaldehyde accumulation → flushing, nausea.
• Medications: H2 blockers, PPIs ↑ gastric pH → ↑ gastric ADH activity? (minor); metoclopramide ↑ emptying.

Clinical Implications

• Food before/during drinking = lower, slower peak BAC.
• Rapid consumption on empty stomach = high peak BAC → greater impairment, toxicity risk.
• Breathalyzer correlates with arterial blood; venous lags.