How does drinking large amounts of ethanol help block enzymatic reaction of methanol to formaldehyde?

Question

If a person drinks methanol, an enzyme in the body (alcohol dehydrogenase) converts it to formaldehyde.

Answer 1

It's the exact same enzyme. It converts methanol to methanal, and ethanol to ethanal, their aldehyde equivalents. Both are bad for you because they just start reacting with with everything around them, but methanal (formaldehyde) reacts twice, and can cause cross-linking of proteins, which is really bad. It essentially "pickles" you--a pickle in an "embalmed" cucumber. Cross-linked proteins are not functional, and in places like your eyes, which don't really actively grow and replace damaged proteins, methanal will lead to blindness. Since both are processed by the same enzyme, you flood it with ethanol so that it doesn't process the methanol allowing it to be excreted, or processes it much slower.