Clinical trials

The goal of this clinical trial is to find out if vitamin D supplements help healthy adults maintain their cognitive and simple physical task performance and emotional state during highly stressful situations. The main question it aims to answer is: \- Does vitamin D help maintain cognitive and physical task performance and emotional state during highly stressful situations? Researchers will compare vitamin D to placebo (a look-alike tablet that contains no active ingredients) to see if vitamin D better maintain cognitive and physical task performance and emotional state during highly stressful situations. Participants will: * Take vitamin D or placebo tablets daily for 8 weeks. * Perform cognitive and simple physical tasks and rate their emotional state under highly stressful situations. * Wear a stress belt that delivers mild electric shocks 1 - 5 times while participants are performing laboratory tasks. * Wear a wristwatch-shaped activity monitor for 9 weeks. * Visit the laboratory 5 times.

This clinical trial aims to evaluate the nature and duration of effects of three FDA-approved medications (propranolol and hydrocortisone) on military-relevant cognitive, emotional, and motor performance following an exposure to a stressful situation (i.e., exposure to a tarantula) in physically healthy adult volunteers (aged 18 - 40) with fear of spiders to help the future development of medications for treating Acute Stress Reactions. The main questions this study aims to answer are: Will placebo treatment (oral placebo) result in significant decrements in Psychomotor Vigilance Task (PVT) performance compared to propranolol treatment? Will placebo treatment \[intramuscular (IM) placebo\] result in significant decrements in PVT performance compared to hydrocortisone treatment? Participants will receive one of five study medications (oral propranolol, oral placebo, IM hydrocortisone, or IM placebo) after a brief exposure to a tarantula. Participants will complete cognitive and simple motor tasks and psychological assessments before and after the study medication administration.

This study is to conduct a clinical trial of tafenoquine combinations to compare the rates of therapeutic efficacy of dihydroartemisinin-piperaquine or artemether-lumefantrine with tafenoquine to chloroquine plus tafenoquine in preventing recurrence of Plasmodium vivax over a 6-month period in adult subjects with uncomplicated P. vivax infection living in Thailand.

The purpose of this study is to determine if brief sounds or tones presented within a restricted period of recovery sleep after a period of sleep deprivation will enhance restorative properties and improve performance during a subsequent period of wakefulness.