Rats exposed to daily doses of morphine experience acute opiate withdrawal which affects the so-called “startle reflex”, which acts as a proxy measure of addiction levels.

Now, researchers at the University of Minnesota have investigated the role of intermittency or continuity of drug delivery in the development of addiction by observing the effects on the startle reflex in animals exposed to morphine at different doses and different times. Their findings suggest that repeated dosing and withdrawal from an opiate drug, which includes morphine and heroin, may play an important role in how addiction in other mammals, including humans, develops.

• Episodic Withdrawal Promotes Psychomotor Sensitization to Morphine
  P. E. Rothwell, J. C. Gewirtz, M. J. Thomas,
  Neuropsychopharmacol. 2010, 35.
  DOI: 10.1038/npp.2010.134