I have never heard sleeping too much referred to as an addiction, but I have seen people who sleep excessively due to depression, anxiety, avoidance of life, exhaustion, medical problems, substance abuse, or exhaustion. Sleeping too much is called hypersomnia as opposed to insomnia which is lack of sleep and a more common problem. The medication effects are different for everyone so he should ask his doctor about that part. Perhaps you can get his permission to speak to his doctor with him and ask your own questions to his doctor. One would also wonder:  How long has this been a problem? Did something happen or change before this problem began? Does he see it as a problem? Does he want to sleep so much? Why? Is there something he wants to avoid while waking? Is he using other drugs or dangerous substances?  Has he had a complete physical examination? Does he have a medical illness that could be contributing to oversleeping? These are some of crucial questions to consider and ask the doctor. Hopefully, this problem will find a solution soon lest he sleep his life away.