Self-administration of caffeine by the rat.

Rats with permanently implanted right jugular vein cannulae were either pre-treated with increasing doses of caffeine for up to 98 h, or underwent no pre-treatment. Both groups were then presented with a lever, the pressing of which caused a self-injection of a caffeine solution. For both groups, some of the rats self-administered caffeine for up to 4 days and then their activity stopped; the other rats did not self-administered caffeine.