[stan_rogers]

Not necessarily. The hangover is primarily a result of the first metabolite of ethanol, acetaldehyde. Some people (predominantly, but not exclusively, Asian and American aboriginal peoples) either lack or are deficient in the ability to produce the enzyme acetaldehyde dehydrogenase. That has two major effects: it encourages hangovers; and for those lucky enough to have the ability to metabolize acetaldehyde to an opioid analogue, it triggers the physical addiction cascade at a much lower level of intake. (Which, by the way, is why Antabuse is utterly ineffective in treating bafflingly hard-core alcoholics. It works by blocking acetaldehyde dehydrogenase, allowing toxic levels to build up in the system. It may bring on near-death hangover symptoms, but it also provides the fuel for an experience not entirely unlike mainlining heroin.)