- Current use of certain prescription medications that may interfere with thermoregulation and/or blood pressure control during heat stress. These include anti-hypertensives (in particular beta-blockers), nitrates and nitrites (e.g. nitroglycerin), PDE5 inhibitors (e.g. Viagra), anticholinergics (e.g. amitriptyline), and alpha-blockers (e.g. Flomax).