This explains the differences really well:
Physical Dependence, Addiction, and Tolerance
As more doctors begin to consider a trial of opioid therapy for patients with chronic noncancer pain, the need to eliminate the stigma, the myths, and the misconceptions that surround these drugs is a priority. Pain specialists have been working toward this goal. The following are some key points about opioid therapy:
Many people confuse physical dependence, which is the occurrence of withdrawal when the drug is stopped, with addiction. Withdrawal is a physical phenomenon that means that the body has adapted to the drug in such a way that a "rebound" occurs when the drug is suddenly stopped. The kind of symptoms that occur include rapid pulse, sweating, nausea and vomiting, diarrhea, runny nose, "gooseflesh," and anxiety. All people who take opioids for a period of time can potentially have this withdrawal syndrome if the drug is stopped or the dose is suddenly lowered. This is not a problem as long as it is prevented by avoiding sudden reductions in the dose.
Physical dependence is entirely different from addiction. Addiction is defined by a loss of control over the drug, compulsive use of the drug, and continued use of the drug even if it is harming the person or others. People who become addicted often deny that they have a problem, even as they desperately try to maintain the supply of the drug.
Addiction is a "biopsychosocial" disease. This means that most people who become addicted to drugs are probably predisposed (it is in the genes) but only develop the problem if they have access to the drug and take it at a time and in a way that leaves them vulnerable. A very large experience in the treatment of patients with chronic pain indicates that the risk of addiction among people with no prior history of substance abuse who are given an opioid for pain is very low. The history of substance abuse doesn't mean that a patient should never get an opioid for pain, but does suggest that the doctor must be very cautious when prescribing and monitoring this therapy.
People with chronic pain should understand the difference between physical dependence and addiction. Unreasonable fears about addiction should not be the reason that doctors refuse this therapy or patients refuse to take it.
Tolerance to opioid drugs occurs but is seldom a clinical problem. Tolerance means that taking the drug changes the body in such a way that the drug loses its effect over time. If the effect that is lost is a side effect, like sleepiness, tolerance is a good thing. If the effect is pain relief, tolerance is a problem. Fortunately, a very large experience indicates that most patients can reach a favorable balance between pain relief and side effects then stabilize at this dose for a long period of time. If doses need to be increased because pain returns, it is more commonly due to worsening of the painful disease than it is to tolerance.
Although opioids can make people sleepy and cloud their thinking, this side effect is usually temporary and long-term therapy is usually associated with normal thinking. Many people fear that taking an opioid will cause them to become "a zombie," unable to function even if the pain is relieved. Fortunately, this is not the case. Most patients can take these drugs for a long period of time and be mentally normal. Patients who have been stabilized on opioid therapy and are clearheaded can drive, work, and do whatever else is necessary.
Opioid drugs are not a cure-all. Although pain specialists now believe that many patients can benefit from this therapy, they also recognize that some patients do poorly. Some patients experience sleepiness or mental clouding that never clears, and still others develop persistent nausea or severe constipation. Some patients actually do not function well when treated with these drugs. Finally, some cannot be responsible drug takers; rarely, a true addiction develops.
For all these reasons, chronic opioid therapy is generally not a first-line treatment for patients with persistent pain. Each patient who is a possible candidate should be evaluated by a professional who is knowledgeable about the use of this therapy.
Patients who receive a trial of an opioid drug should expect to be carefully monitored by their physicians. Any patient given opioid drugs to treat pain should follow the doctor's prescription exactly. Patients should never increase the dose on their own. They should never go to another physician to get prescriptions and should always be completely honest in reporting the effects produced by the drug.
The physician will inquire about pain relief; side effects; the ability to function physically, psychologically and socially; and the occurrence of any behavior that suggests problems in controlling the medication. For some patients, very intensive monitoring is appropriate; for others, monitoring can be less intensive.
Some doctors will want the patient to agree to a contract that describes the patient's responsibilities when taking the drug. Some physicians will even want to monitor the patient's urine to make sure that the patient is taking only the drugs that should be taken. A physician may want these things to feel secure in the knowledge that the patient is appropriately using the drug. When the physician is able to have this security, he or she is free to act in the patient's best interests. A good relationship between the physician and patient is needed for long term opioid therapy to be successful.
The drugs that are now used to treat chronic pain include morphine, hydromorphone, oxycodone, fentanyl, methadone and others. Some opioids, like codeine and hydrocodone, are usually prescribed in combination with acetaminophen or aspirin. Although the latter drugs are sometimes used for chronic pain, long-acting drugs are generally preferred. These long-acting drugs can be taken twice a day, once a day or, in the case of the fentanyl, by patch.
Although some people believe that opioid drugs are only appropriate for certain kinds of pain, doctors are unable to accurately predict which pain problems will not respond.
Each opioid produces a different range of effects in each individual. The same person may get too sleepy from morphine but experience very little sleepiness from oxycodone, or vice versa. For this reason, many pain specialists are now suggesting that patients with chronic noncancer pain be given an opportunity to try different commercially available opioid drugs in order to find the drug that produces the most favorable balance between pain relief and side effects.
Regardless of the opioid, the dose often has to be adjusted to get the best effect. Patients should understand that adjustment of the dose and the use of other medicines, like laxatives, to treat side effects are a common part of therapy.
http://www.stoppain.org/pain_medicine/content/medication/opioids.asp#physical (copied the above this site/url)
http://www.stoppain.org/- main website with above info
