Levamisole is one of those drugs that was discovered quite awhile ago, when we had even less idea what target things were hitting. It’s not used often in people these days. What’s interesting about it is that it is occasionally found as an adulterant in cocaine (PDF) – and it popped up again recently.
It is truly bizzare what people use to cut drugs. I once heard of a chemistry professor who told his class about how he walked into a head shop and saw a big sack of mannitol behind the counter (which is used as a cutting or bulking agent for street drugs as well). He marvelled that he had just bought mannitol from Aldrich for his lab (presumably for more mundane, licit purposes) and that the shop was charging much too high a price. So, if you were thinking of saving on lab supplies at the bong store, that’s right out.