The Cruise lines have 3 primary reasons for requiring the medical exam:
1. Being self-insured, we don't want to take the chance that you have an undiclosed medical condition that could result in us paying to care for you for the rest of your life. Some people try to get jobs on ships only to later disclose a pre-existing medical problem that the cruise line has to pay for.
2.Most crewmembers have safety duties in any emergency. We must ensure that you are healthy and fit enough not only to save your own life, but also the lives of our passengers.
3. Safety duties also require crewmembers who are reliable and not subject to substance abuse that could impair their performance. We test extensively for drugs and alcohol. Any signs of illegal drug use or abuse of alcohol will get you rejected. This is the point where the majority of American applicants fail.