A young college student, who is down and out on his luck, hitches a ride with a couple weird doctors. They offer him cash if he agrees to let the dr's use him for medical experiments for the weekend. He agrees. This movie takes place over the whole weekend. The student finds that a friend of his has had his head attached to a pigs body and realizes that he may be next. It seems like an older movie, filmed possibly in Europe. Prolly filmed in 70's is my guess. Any info greatly appreciated
This sounds like O Lucky Man!, a 1973 British horror film. The synopsis here includes bits about human heads on pig bodies as well as several other of the plot points you mentioned.