Can addiction be treated successfully?
Yes, addiction is a treatable disorder. Research on the science of addiction and the treatment of substance use disorders has led to the development of research-based methods that help people to stop using drugs and resume productive lives, also known as being in recovery.
Source: National Institute on Drug Abuse
Does relapse to drug use mean treatment has failed?
No. The chronic nature of addiction means that for some people relapse, or a return to drug use after an attempt to stop, can be part of the process, but newer treatments are designed to help with relapse prevention. Treatment of chronic diseases involves changing deeply rooted behaviors, and relapse doesn’t mean treatment has failed. When a person recovering from addiction relapses, it indicates that the person needs to speak with their doctor to resume treatment, modify it, or try another treatment.
Source: National Institute on Drug Abuse
Can physical illness affect mental health?
Yes. Being physically unwell can affect people mentally. 
Is recovery possible for people with a mental illness?
Most, if not all, people with a mental health condition are relieved from their symptoms through an effective treatment plan which may include medication, peer support groups, and psychotherapy. Early detection and treatment or intervention are key to recovery. Many people with mental illnesses who are diagnosed and get treated respond well.
Is it okay to stop taking medications when I feel better?
The simple answer is no. Symptoms may return or even get worse when you stop medicating. It is also important to let your doctor know if you plan or have stopped your medications and the side effects you are experiencing so he or she can adjust your medication dosage.