Withdrawal. If someone takes any opiate regularly, whether hydrocodone (the opiate in vicodin) or heroin, they will eventually become dependent on the medication, if they are taking enough of it long enough. The symptoms are those of withdrawal, which feels like having the flu -muscle aches, headache, nausea, vomiting, diarrhea, hot and cold chills, sweating and others. If you are concerned, get help.
Addiction. A chronic compulsion to get the drug. Getting the drug becomes the focus of your day. You neglect freiends and family to get the drug.