Analgesic tolerance refers to the diminishing analgesic effect of an opioid because of physiological adaptation to the opioid. Analgesic tolerance is not inevitable, but it does occur.
The dose of an opioid such as morphine typically can be increased to overcome any tolerance that may develop, as long as side effects are tolerated.
Analgesic tolerance should not be confused with the need to increase dose because of an increase in pain.
Reference: Pain & Policy Studies Group. Glossary of Terms. Internet. Accessed June 20, 2009. Available at http://www.painpolicy.wisc.edu/glossary.htm