What are caffeine’s main benefits?

Caffeine restores alertness and wakefulness, and reduces drowsiness during mental fatigue.^[1][2][3] It also improves several aspects of cognitive function — accuracy, reasoning, memory, reaction time, attention, etc. — during cognitively and/or physically demanding tasks.^[4][1][2][3] Furthermore, caffeine can improve some aspects of cognitive function that have been impaired by acute sleep deprivation.^[2][3]

Caffeine can also help with pain relief. For example, when caffeine is added to analgesic (pain relieving) drugs like acetaminophen (also known as paracetamol) or ibuprofen, there is a small but clinically meaningful improvement in pain.^[5][6]

In hospitals, caffeine (typically caffeine citrate) is used to treat apnea (temporary cessation of breathing) in premature babies, but both the optimal dosing strategy and caffeine’s effect on survival and subsequent neurocognitive development are unclear.^[7] Furthermore, in people with asthma, caffeine may have a small beneficial effect on some aspects of respiratory function (forced expiratory volume in one second, FEV1, and mid-expiratory flow rate) for up to four hours.^[8] However, this effect also has implications for asthma diagnostics because prior caffeine ingestion may reduce the accuracy of lung function tests.^[8]

Caffeine can raise whole-body fat oxidation rates, both at rest and during exercise,^[9][10] and increase daily energy expenditure,^[11][12] but these effects are negligible — approximately 400 kilojoules or 100 kilocalories per day. The effect of caffeine on appetite regulation and energy intake is less clear and varies depending on factors like timing and dose.^[12][13] Consequently, the role of caffeine in weight loss and/or weight management is unclear. Despite one meta-analysis concluding that caffeine can promote reductions in weight, BMI, and body fat,^[14] its utility is limited because the included trials used energy-restriction diets and/or ephedrine, a powerful stimulant that causes weight loss.

Caffeine is widely used in sports because it can improve both aerobic and anaerobic performance in trained and untrained individuals.^[15] For example, when taken before or during exercise, caffeine has small to moderate-sized effects of lowering the rating of perceived exertion (RPE)^[16][17] and improving aerobic endurance, anaerobic power, sprint speed, muscle endurance, muscle strength, muscle power (jump height), and agility.^[15][18][19] These effects are found across a range of sports (running, cycling, and swimming, etc.) including skill-based team sports (e.g. basketball, soccer, etc.).^[15][20][21] Furthermore, when taken before and/or during exercise, caffeine may also improve cognitive functions, such as attention, reaction time, memory, and feelings of fatigue.^[1] One drawback is the predominance of research studies that only included young male participants.^[18][15] Some meta-analyses find similar performance benefits in females to those found in males,^[22][23][24] but more randomized controlled trials in females are needed to substantiate the generalization of sports nutrition recommendations for caffeine.^[15][25]