Figure 5.3. Metabolism of alcohol in the liver. Most of the alcohol that is ingested is metabolized in the liver in the two steps shown below. Alcohol is coverted to acetaldehyde by the enzyme alcohol dehydrogenase (ADH). Then the acetaldehyde is converted to acetic acid by the enzyme aldehyde dehydrogenase (ALDH). Polymorphisms at both the ADH and the ALDH loci can influence the susceptibility to alcohol abuse and dependence.