During each study session participants will be asked to smoke a cigarette. The cigarette may contain marijuana or it may contain placebo (a blank). Participants will also be asked to swallow a capsule 2-hours prior to smoking the cigarette. The capsule could contain placebo (a blank), THC (delta-9 tetrahydrocannabinol, which is the active ingredient in marijuana responsible for its mood effects), or d-amphetamine. We will have participants answer questions about how the drugs make them feel and measure their vitals signs (blood pressure, heart rate, and oxygen saturation) will be measured using a non-invasive (external) vitals monitor.