This is the reason ethanol is often used in emergencies as antidote for methanol or glycol accidental ingestions.
Heavy drinkers exhibit a continuous production of high level of dehydrogenase (definition framed here) for years or decades, production triggered in human body only by the consumption of ethanol.
Ethanol is as toxic to humans as methanol but by raising the production of dehydrogenase, the human body can metabolize it.
In the same time ingestion of alcohols other than ethanol generally does not trigger production by the human body of enough of the protecting ADH, thus their very toxic effect.
Both situations are due to genetic factors accumulated by human and other species throughout evolution.
Throughout the whole period of heavy drinking the human body does not need its immune system for fighting against methanol producing bacteria that live in the gut because the methanol produced by those is also metabolized by the ADH of which production is triggered by the ethanol from drinking (and maybe permanently reallocates those resources for producing dehydrogenase for metabolizing both ethanol and methanol and other alcohols produced by the bacteria in the gut or coming from a polluted environment).
It is possible that the immune system by not being used to fight that type of bacteria for so long looses the capacity of fighting it.
That's why they probably can not stop, because of the terrible hangovers given among other things by the methanol produced by those bacteria without the presence of ADH "normally" triggered by drinking alcoholic beverages, bacteria that their immune system abandoned fighting or forgot recognizing.
Maybe the solution could be as simple as vaccination against those so the immune system start recognizing them again.
ADH is always present in healthy individuals in amounts that insure protection against the amounts of all types of alcohols normally present in food. Although only ethanol raises ADH production, the other alcohols present in food or generated by other alcohols production microorganism are always reasonably proportional. Probably ethanol is most common and that's why the human body uses it as trigger in raising ADH production.
By overstimulating the production of ADH with heavy alcohol consumption it is also possible that the production mechanism to be depleted by overuse and/(or more likely) the triggering amount necessary for starting production to become permantely raised so the normal amounts present in food or generated by ethanol or other alcohols producing microorganism living in the gut do not trigger its production before (relatively low) toxic levels are being built, giving hangovers. In this case due to lack of further knowledge, all i can say is it can be imagined a lifelong treatment that may include ADH or other medication that can stimulate the production of it at normal levels.
