The signs of alcoholism include an inability to control your drinking, withdrawal symptoms when you attempt to stop drinking, and continued cravings to drink even when it negatively affects your life.
Drug addiction has been classified as a disease by the medical community. Just like any other health-related condition, addiction needs to be appropriately treated as an illness by qualified professionals.
The goal of an intervention is to convince the person to get treatment for their problem. An intervention should be well planned, and it should involve those who are close to the subject of the intervention.