RUSH, also known as rushpoppers, is a type of substance that has a history of abuse as a recreational drug, particularly in the United States during the 1960s and 1970s. Inhalation of rushpoppers has the ability to relax smooth muscles throughout the body, which can alleviate sensations of pain. Smooth muscles surround blood vessels in the human body, and their relaxation can cause blood vessels to expand, increasing heart rate and blood flow, resulting in a feeling of warmth and excitement.