I've read about treatments for methanol poisoning and found that ethanol helps methanol bypass metabolism, thus preventing it from forming forming methanol acid and formaldehyde, sparing you serious harm. This makes sense to me, but it does raise the question; why would you bother denaturing ethanol with methanol? Seems like a waste of methanol to me. Typical methylated spirits is 95% ethanol and 5% methanol (apparently). According to wikipedia it takes about 10 ml of methanol to permanently damage the optic nerve. To ingest 10ml of methanol from methylated spirits one would have to consume 200 ml in a short period of time. At that point you will also have consumed 190 ml of pure ethanol which is far higher than a recreational dose and would probably render a lot of people unconscious anyway if consumed quickly.
Also this dose is far sufficient to treat methanol poisoning, a blood concentration of 100-150 mg/Dl is used to treat methanol poisoning and can be acheived with 48 ml of ethanol for a 70 kg person. Of course ethanol is not a 100% effective antidote, but the levels of methanol that would be ingested alongside a more appropriate dose of ethanol seem somewhat insignificant to me.
It doesn't add up to me. If anyone can explain to me why methanol is still used, and / or why I am wrong and explain how it is still harmful that would be great.
Also, just to clarify, I have no intention of drinking metho. In fact the methylated spirits you can buy in my area don't contain methanol, they contain various other undisclosed denaturants