Pain-Relieving Dose of Aspirin for Adults
For acute pain relief in adults, aspirin 600-650 mg orally every 4-6 hours is effective, with a maximum of 4000 mg (48 tablets of 81 mg or equivalent) in 24 hours 1, 2.
Dosing for Analgesic Effect
The evidence clearly demonstrates a dose-response relationship for aspirin's analgesic properties:
- 600-650 mg: This is the standard analgesic dose with an NNT (number needed to treat) of 4.2 for at least 50% pain relief over 4-6 hours 3, 4
- 900-1000 mg: Slightly more effective with NNT of 3.8, but increased adverse effects 3
- 1200 mg: Most effective with NNT of 2.7, but highest risk of side effects 3
The optimal balance of efficacy and safety is achieved with 600-650 mg doses, which can be repeated every 4-6 hours as needed 1.
Practical Administration
According to FDA labeling, adults and children 12 years and older should:
- Take 4 to 8 tablets (of 81 mg each = 324-648 mg) every 4 hours
- Not exceed 48 tablets in 24 hours (approximately 4000 mg)
- Drink a full glass of water with each dose 2
Important Caveats
Lower doses (75-162 mg) are NOT effective for pain relief 3, 4. These low doses are used for cardiovascular prevention, not analgesia. The research shows that doses below 600 mg do not provide significant pain relief compared to placebo 3.
Common side effects at analgesic doses include:
- Gastric irritation (NNH 38 for 600-650 mg)
- Drowsiness (NNH 28 for 600-650 mg)
- Nausea and vomiting 3, 4
Contraindications to Aspirin Use
Do not use aspirin for pain in patients with:
- Aspirin allergy or hypersensitivity
- Active bleeding or bleeding disorders
- Recent gastrointestinal bleeding
- Active peptic ulcer disease
- Severe hepatic disease
- Concurrent anticoagulant therapy
- Age under 21 years (Reye's syndrome risk) 5, 6
Alternative Considerations
For patients requiring pain relief but unable to take aspirin, ibuprofen 400-600 mg every 4-6 hours is an appropriate alternative NSAID with similar efficacy 1, 7. The evidence shows that NSAIDs as a class provide comparable analgesia milligram-for-milligram 3, 4.