Is it generally a good idea to stick drugs up your butt?
this is a serious question
In general, rectal administration of drugs implies some changes in its distribution and effects. A higher proportion of the drug reaches brain without passing through liver an it produces a faster onset, shorter peak, and shorter duration than the oral route. The absorption can be conditioned by the presence and quantity of faeces in rectum and colon, but in general dosages should be 10-20% lesser than oral route. In moderate use and using hygienic measures risks should not be different to oral route and there are no communicated cases of serious adverse effects using this route (although it is not very common). Not every drug is suitable for this method, but morphine, cocaine and amphetamine derivatives work.
This is a serious answer.