While it's true that using opioid pain medications, such as morphine, long term can sometimes increase a patient's tolerance and physical dependency of the drug, actual addiction is rare.
Tolerance occurs when the body adapts to the current dose of a medication. Tolerance of opioid pain-relieving effects is uncommon, but tolerance of the medication's side effects is common and desirable. Most patients remain on a stable dose of a pain medication for long periods of time. An increase in an opioid dose is most often related to disease progression, rather than tolerance.
Physical dependency is more common and usually occurs 3 to 4 weeks after starting an opioid. Dependency is usually noticed when the medication is stopped abruptly and the patient has symptoms of withdrawal.
Neither tolerance nor physical dependency should be confused with addiction. Opioid addiction is a compulsive craving for a drug for effects other than pain control. It's extremely rare in patients with life-limiting illnesses. Even for patients outside of the palliative care and hospice settings, studies have shown that addiction is rare and almost never occurs in patients who don't have a history of drug abuse.
Source:
Ferrell, BR and Coyle, N. Textbook of Palliative Nursing, second edition. Oxford University Press, 2006.
