The first two are normal physical phenomena that happen in ALL patients who take heavy doses of narcotics, but only the last one is abnormal/pathological. Thus, if you claim your character is addicted, his or her behavior should show at least a few pathological psychological features (bad relationships, inability to hold a job, stealing to pay for fixes, lying to doctors for drugs, etc.).
You don't become physiologically tolerant and/or physically dependent on ALL drugs. Thus, you don't necessarily go through withdrawals when you come off certain controlled substances (e.g. hallucinogens like marijuana and PCP don't cause withdrawals). And not all withdrawal symptoms are the same. They depend on the drug in question. E.g. withdrawals symptoms and overdose treatment for alcohol/benzodiazepines/ barbiturates are similar. However, the symptoms of stimulant withdrawal and overdose will be totally different. The point is the writer needs to research the specific overdose and/or withdrawal symptoms for the individual drug his or her character is hooked on.
Only SOME people are susceptible to addiction to controlled substances (don't make the mistake of thinking that ALL people who take controlled substances eventually become addicted). People susceptible to addiction tend to exhibit addictive tendencies early on (teenage or young adult addictions to smoking, alcohol, etc). In general, young people are more susceptible to developing addiction because their coping skills aren't yet developed and they can learn to rely on drugs for dealing with the underlying anxiety that leads them into addiction.
I see many elderly people with severe, painful joint pathology who don't want to take narcotics b/c they're afraid of getting addicted. But if they've taken narcotics periodically during their lives for e.g. root canals, fractures, etc, and have never had a problem getting off the drugs, they're at lower risk for addiction. As noted above, though, they will (especially if they're on large doses) eventually become physically dependent).
There's a difference between pain and suffering. Pain happens when an inciting event causes pain receptors to fire (e.g. a burn, a sprain, a pulled muscle, etc.). However, that physical pain is interpreted by the brain in the context of the person's emotional state. A highly anxious patient or one with a volatile psych history (history of abuse, etc.) is more likely to experience psychological "suffering" with a low level of pain.
Thus, if the person tries to medicate his or her subjective experience with pain using pain pills, he or she is likely to over-medicate to quell the anxiety. You're not supposed to treat your anxiety with pain pills. That's how you become addicted. Many, many chronic pain patients suffer with psych issues, and often those psych issues long pre-dated their chronic pain. Psych issues are a definite risk factor for chronic pain and addiction.
Dr. Rita Hancock, a full-time physician and author of Christian health books, writes about how emotional and spiritual factors contribute to physical disease through the mind-body-Spirit connection. According to Dr. Rita, “Once these underlying barriers fall away in the healing light of God’s truth, patients automatically feel less physical pain, experience fewer stress-induced symptoms, lose weight, and shed addictive behaviors more easily.” Dr. Rita is the author of The Eden Diet (Zondervan, 2008) and an as-yet untitled release with Charisma House, pending January 2013. She resides in Oklahoma City with husband Ed, and two wonderful children, Lindsey and Cory.