GABA is an inhibitory neurotransmitter that is found primarily in the brain. High GABA levels result in low levels of dopamine, another neurotransmitter that is the brain's "feel good" chemical and which plays a primary role in cocaine drug addiction. Cravings for cocaine can be reduced by lowering dopamine levels. This makes GABA-altering medications a potential treatment for cocaine addiction. This study will involve five GABA enhancing medications: tiagabine, topiramate, valproic acid, baclofen, and progesterone. The purpose of the study is to evaluate the interaction between GABA medications and cocaine in terms of safety and craving responses. In turn, these findings may guide future cocaine pharmacotherapy trials.