Drug continuation after an RCT ends

Suppose a new treatment is investigated in a Randomized Clinical Trial and the treatment turns out to be a very effective, life changing medication for a particular illness for a participant. What happens once the RCT ends in terms of continuing access to that particular drug (that was so effective) for particular patients? Does anyone have insight on ethical/legal obligations for a patient to continue on with the drug? How can a patient continue on the RCT drug once the RCT ends?