Self-administration of phentermine by naive rats: effects of body weight and a food delivery schedule.

Food deprivation has been shown to increase intravenous self-administration of amphetamine and cocaine. In the present experiment, the response rates of four groups of eight rats for intravenous infusions of phentermine under free-feeding (FF) and 80% free-feeding weight (FFW) conditions in the presence and absence of a fixed time 1 min (FT-1) food delivery schedule, were compared with those of saline reinforced animals under identical conditions. The findings showed that: (1) Overall, response rates of phentermine-reinforced animals were significantly greater than were those of saline-reinforced animals; (2) 80% FFW animals self-injected significantly greater amounts of phentermine than did FF animals; and (3) the operation of an FT-1 schedule failed to affect the rate of phentermine-reinforced responding.