Psychologist:
Many people have a hard time understanding the difference between a psychologist and a psychiatrist. A clinical psychologist has a doctorate degree in psychology and must be licensed by the state in order to diagnose and treat patients. A psychiatrist goes to medical school and specializes in psychiatry. A psychologist has a high level of training to help people overcome mental health issues. Some psychologists specialize in substance abuse or addiction treatment. A psychologist can very helpful when staging an intervention. A psychologist also works one-on-one with a recovering addict while in treatment.
MS:
A master of science (MS) is an advanced degree, usually in the natural sciences, mathematics, engineering, agriculture and computer science. There are multiple MS degree program options in the fields of mental health, psychology and counseling. A master's degree is often required to become a licensed therapist, counselor or social worker. Someone with an MS in mental health counseling might practice as a rehabilitation counselor working with patients struggling with substance abuse or addiction. MS programs vary by the college or university, but typically involve hands-on learning.
Ph.D:
A Ph.D, also known as a doctoral degree, is one of the most advanced academic degrees there is. It can take 4-8+ years to complete a Ph.D program. Getting a Ph.D involves advanced training in research and evaluation (i.e. looking at other research studies that already exist and making connections between them), as well as completing original research in the form of a dissertation. A person can hold a Ph.D in addition to other degrees, so for example you can be an MD with a Ph.D or LPC with a Ph.D. Some people with Ph.Ds can specialize in substance abuse rehabilitation. Those with doctoral degrees are generally held in high regard within the academic and wider community (they have a lot of prestige), and generally charge higher prices for their services if they are in private practice. They do not generally help with interventions.