Just read up the machinist - looks like a good movie. Apparently, Christian Bale ate an apple or a can of tuna and one coffee a day for 4 months to lose 28kg for the role.
As to the opiates, my understanding is that you can get withdrawal symptoms after as little as a few weeks of use on proscribed dosage. I was on maximum dosage for two different opiates as only way to cut through the pain and for a fair bit longer than two weeks.
