Limited research has been done on the effects of gender and menstrual cycle in response to drugs of abuse in humans. The main goal of this pilot study is to investigate the safety and tolerability of progesterone treatment in female nicotine users. In addition, plasma progesterone levels reached with a single 200 mg dose of progesterone treatment will be measured. The study will be a double-blind placebo controlled, crossover trial in which 12 female smokers who are in the early follicular phase of their menstrual cycle will be enrolled. Druing the experimental sessions, subjects will be given a single 200 mg dose of micronized progesterone or placebo and multiple blood samples will be obtained to measure the plasma levels of progesterone. Starting 2 hours after progesterone or placebo treatment, subjects will have a self-administration period that will last around 2.5 hours. We hypothesize that administration of 200 mg of progesterone will achieve plasma progesterone concentrations similar to those found in the luteal phase of the menstrual cycle, 3-30 ng/ml.