Caffeine anhydrous is the powdered form of caffeine, a central nervous system (CNS) stimulant that reportedly prevents drowsiness and fatigue. It is commonly used in weight-loss supplements because the powder is less voluminous and can be easily integrated with other powders in proprietary blends. There is virtually no difference between caffeine's powdered or liquid forms, although some diet companies may claim caffeine anhydrous is absorbed more quickly by the body.

Chemically, caffeine occurs naturally in plants, especially in seedlings that are beginning to produce roots or leaves. It helps plants grow by preventing insects from eating the plant's leaves or roots, by paralyzing and killing them. The highest levels of caffeine occur in coffee bean seedlings and cocoa beans. Guarana plant seedlings also contain a substantial amount of caffeine.

Caffeine anhydrous is obtained by harvesting these beans and seedlings, drawing out the caffeine extract, and boiling it at high temperatures until the water is drawn out. This produces a white, crystalline powder, or its anhydrous form. This powder is then combined with others, molded into tablets or put into capsules and sold. It may also be found in powdered form, although it is more commonly found in pills.

Its effects on the body are similar to the consumption of liquid forms of the substance. It is first absorbed by the tissues in the stomach and small intestine, where it filters off to other parts of the body. Its most significant effect is its ability to stimulate the CNS, which processes information sent from other areas of the body. This temporarily prevents the affected person from feeling tired, while improving alertness. It also speeds up the heart rate and increases exercise endurance, effects commonly sought out by athletes and bodybuilders.

Diet and energy supplement companies commonly use caffeine anhydrous because of its stimulant effects. Some diet companies claim it can also suppress appetite and increase metabolism. These assertions are not clinically backed by any major study, however.

Caffeine anhydrous can cause numerous side effects. Studies have shown it can induce blurred vision, dizziness, dryness of the mouth, and gastrointestinal discomfort. It can also make people feel more anxious or irritated, due to its effects on the central nervous system. Its effects on the heart are well documented, and even moderate use can cause an abnormally fast heart rate.

Taking more than 300 milligrams (mg) of caffeine anhydrous can lead to a health condition called caffeine intoxication. This can drastically affect a person's reasoning ability, and lead to nervousness, rambling speech patterns, muscle twitching, and agitation. Larger overdoses can lead to episodes of mania, disorientation, hallucinations, and, in serious cases, psychosis.