Chronic marijuana use is associated with numbers of chronic problems such as lung disease, emphysema, several types of cancer and mental decline. If there is any way that your friend will let you help, there are numbers of organizations that would be able to assist him on getting off this dangerous drug. It is also associated with obesity, increased body hair, high blood pressure, infertility, and diabetes. Recently, we have found medications, such as aldactone, which can be helpful. There are medical, moral, and religious considerations.
Creatine appears to be helpful to only a limited number of athletes.
Taken in very high doses, it may be harmful. I always recommend that these types of supplements be taken under a doctor's supervision. In this case, a sports medicine physician may be helpful for you. Then four years of medical school and then 3-5 years of residency training. Most medical physicians do not begin practice until they are 29 or 30 years old.