The features and effects of the following ergolytic drugs are examined: tobacco, alcohol, caffeine, and antihistamines. Research has shown that the nicotine present in tobacco is an addictive drug and is the key ingredient in cigarettes and smokeless tobacco products ("chew"). Nicotine is a central nervous system stimulant that relaxes skeletal muscles, constricts blood vessels, and increases heart rate and blood pressure. It can cause coronary artery spasm and lower the threshold for ventricular fibrillation; death has been reported in athletes who use smokeless tobacco following vigorous exercise. Research has shown that alcohol in a person's system impairs motor skills, including reaction time, balance, accuracy of movement, hand-eye coordination, and complex coordination. Caffeine is a central nervous system stimulant and one of the most popular mildly addictive drugs in the world. Caffeine's strongest effects are felt for about 1 hour after ingestion, but some effects last 4 to 6 hours. As a diuretic, caffeine prompts the body to lose water through urination, which can lead to dehydration and impairment in the course of physical exercise. Antihistamines are common in over-the-count medications. The most common side effects include decreased ability to concentrate, increased reaction time, and sleepiness. Although eliminating the use of ergolytic drugs will not eliminate the physical and mental effects that stress causes - such as heart rate increase, tunnel vision, auditory exclusion, and loss of dexterity - it does enable officers to keep these debilitating effects within a range that permits optimal performance under stressful conditions.