Actually, paracetamol seems to be less toxic if taken while drunk, but more so if taken the day after. The enzyme (a cytochrome P450 oxidase) that transforms paracetamol to the toxic substance (N-acetyl-iminoquinone) can also oxidize alcohol. If there is alcohol present, the transformation of paracetamol goes slower and/or by other routes, so taking it while drunk leads to lower blood concentrations of N-acetyl-iminoquinone*. However, when there is alcohol present, the liver produces more cytochrome P450 to detoxify it quicker, and that surplus is still there the day after, so the degradation of paracetamol to N-acetyliminioquinone is faster, making paracetamol more toxic. So don't use it to combat hangovers.
*This have been investigated in a double-blind experiment, where people either got a alcohol-contaning og non-alcoholcontaining intravenous drop (IIRC). When I first read this article, I was rather amused about the idea that people should be unable to tell the difference, but placebo intoxication seems to be rather powerful.