Many substances and medications ingested by humans exert neurotoxic or psychoactive effects on the central nervous system (CNS) that may be subjectively experienced as symptoms of anxiety. Some classes of substances, including caffeine, amphetamines and other stimulants (e.g., cocaine), cannabis, phencyclidine, and hallucinogens (e.g., LSD), exert these effects directly. That is, when ingested, these substances raise levels of nervous system and physiological activity (e.g., increased heart rate, respiration, blood pressure, alertness), which can be experienced as a subjective feeling of anxiety or panic. Other substances that can act in this way include some pain and antidepressant medications, anesthetics, oral contraceptives, “nondrowsy” antihistamines, heart and blood pressure medications, bronchodilators and others including heavy metals (e.g., mercury) and some insecticides. Some substances, including alcohol, sedatives, hypnotics, opioids, ...