Valerian was used in ancient Roman and Greek as a cure for insomnia, and recent scientific research suggests it still may be useful for that purpose. Some research suggests that valerian may improve sleep quality through a reduction in cortical excitability, meaning it can relax your brain's response to stimuli. Other research has found that when humans are placed in high-pressure situations, consuming valerian may result in a smaller increase in systolic blood pressure and lower perceived stress.