What it is
Regulatory status: common food constituent and dietary supplement ingredient; also used in some approved medicines
Mechanism evidence: human
At a glance
What it is, why people use it, the evidence, and what to know before trying it.
Why people use it
- Alertness
- Exercise performance
- Reduced perceived fatigue
Evidence at a glance
Caffeine reliably improves alertness and can support exercise performance, but delaying it 90–120 minutes after waking is a personal timing strategy rather than an established universal rule. Total dose and distance from bedtime matter more for safety and sleep.
Confidence: strong
Safety & interactions
Known side effects, interactions and use limits from reviewed sources.
Caffeine can cause anxiety, tremor, palpitations, reflux and sleep disruption. Concentrated powders create overdose risk. Pregnancy, cardiovascular conditions and interacting medicines may require lower individualized limits.
- Known caffeine-triggered arrhythmia without clinician guidance
- Use near bedtime when sleep is affected
- Insomnia
- Anxiety
- Tremor
- Palpitations
- Headache or withdrawal
- Other stimulants
- Some CYP1A2-inhibiting medicines
Forms and variants
This review does not automatically apply to:
- caffeinated multi-ingredient pre-workout blends
- pure bulk caffeine powder treated as a normal serving