RecruitingDrug trialEffects of 5HTP on the Injured Human Spinal CordThis study will assess how the serotonin precursor, 5-HTP, alter nervous system excitability and motor function in individuals with spinal cord injuries of differing chronicity and severity. Participants will visit the lab on 4 separate occasions where they will be administered four different drugs in a randomized, double-blinded, placebo-controlled crossover design.