Spontaneous Opiate Addiction in Rhesus Monkeys.

Spontaneous drug-seeking behavior was established in 3 out of 4 rhesus monkeys that were given unrestricted access to morphine and placebo solutions. The monkeys were kept in their home cages throughout the experiment and were not subjected to conditions of stress; prior addiction was not established by the usual injection procedures. The animals became physically dependent on the drug and showed abstinence symptoms when injected intramuscularly with nalorphine (N-allyl normorphine hydrochloride). This method may be useful for studying individual differences in susceptibility to drug abuse.