These are stimulants used primarily to delay the onset of mental and physical fatigue. Students studying long hours for exams, athletes who feel the drugs will improve their performance, and workers who want to stay awake on the job often use stimulants. These drug compounds are often found in diet pills which, if misused, can lead to anorexia nervosa. Anorexia nervosa is a pathological loss of appetite thought to be psychological in origin that is manifested in extreme dieting and excessive thinness. Caffeine is also found in many beverages, pain medications, and allergy and cold remedies.
Environmental factors such as the availability of marijuana, expectations about how the drug would affect them, the influence of friends and social contacts, and other factors that differentiate identical twins’ experiences also were found to have an important effect; however, it also was discovered that the twins’ shared or family environment before age 18 had no detectable influence on their response to marijuana.