Aspirin: Uses, Dosage, Side Effects and Interactions

Aspirin, also known as acetylsalicylic acid, is one of the most widely used medications worldwide. With a history stretching over a century, its reputation as a pain reliever has been joined by roles in preventing heart attacks, strokes, and even certain cancers. But behind its everyday use are evolving recommendations, nuanced dosing strategies, and a complex risk-benefit landscape. In this article, we’ll unravel the science-backed uses, best practices for dosage, potential side effects, and key drug interactions of aspirin, helping you navigate its benefits and risks with confidence.

Uses of Aspirin

Aspirin’s versatility makes it a staple in both medicine cabinets and clinical settings. Beyond being a go-to for headaches and muscle aches, aspirin’s preventive power in cardiovascular and cancer care has been the subject of intense research and shifting guidelines. Understanding these uses helps ensure the right patients get the right benefit—without unnecessary risk.

Use	Main Purpose	Typical Population	Source(s)
Pain Relief	Analgesic, anti-inflammatory	General adult population	14 15
Cardiovascular Prevention	Reduce heart attack/stroke risk	Adults with/at risk for CVD	1 3 5 11 12
Cancer Prevention	Reduce colorectal cancer risk	Adults 50-59 at higher risk	1 2
Thromboprophylaxis	Prevent clots post-surgery	Orthopedic patients	4 8 10
Preeclampsia Prevention	Lower risk in pregnancy	Pregnant women at high risk	6
Aspirin-Exacerbated Resp. Disease	Symptom control	Patients with AERD	7

Table 1: Major Clinical Uses of Aspirin

Pain and Inflammation

Aspirin’s classic use is as an analgesic and anti-inflammatory agent. It blocks enzymes involved in prostaglandin synthesis, providing relief for headaches, muscle pain, minor arthritis, and fever 14 15. While other nonsteroidal anti-inflammatory drugs (NSAIDs) are now more commonly used for chronic pain, aspirin remains a trusted option for acute symptoms.

Cardiovascular Disease Prevention

Aspirin’s role in reducing the risk of heart attacks and strokes is well-established for people with known cardiovascular disease (secondary prevention) 5 9. For adults without established disease (primary prevention), the benefit is more modest and must be weighed against the risk of bleeding. Guidelines recommend low-dose aspirin for certain adults aged 50-59 with a 10% or greater 10-year CVD risk, provided they have no increased bleeding risk and are willing to take aspirin daily for at least 10 years 1. For those 60-69, the decision is individualized 1. In diabetics, aspirin modestly reduces serious vascular events but increases bleeding risks, making the net benefit marginal 11 12.

Cancer Prevention

Long-term, low-dose aspirin can lower the incidence of colorectal cancer and its recurrence, especially in higher-risk adults 1 2. The reduction in overall cancer incidence may be up to 10% after 10 years of continuous use, but these benefits do not always outweigh the risks in average-risk populations due to bleeding concerns 2.

Thromboprophylaxis After Orthopedic Surgery

Aspirin is increasingly used to prevent blood clots (deep vein thrombosis and pulmonary embolism) after hip and knee replacements 4 8 10. Its cost-effectiveness and safety profile—especially at low doses—make it a viable alternative to other anticoagulants in many patients.

Preeclampsia and Fetal Growth Restriction

Low-dose aspirin, started early in pregnancy, can reduce the risk of preeclampsia and fetal growth restriction in women at high risk 6. The greatest benefit is seen when aspirin is initiated before 16 weeks of gestation.

Aspirin-Exacerbated Respiratory Disease (AERD)

For patients with AERD (asthma, nasal polyps, and aspirin sensitivity), aspirin desensitization followed by regular aspirin therapy can significantly improve symptoms and reduce corticosteroid requirements 7.

Dosage of Aspirin

Selecting the right aspirin dose is crucial to maximizing benefit and minimizing harm. Recommendations vary depending on the indication, patient profile, and risk factors.

Indication	Typical Dose (mg/day)	Special Notes	Source(s)
Pain/Fever	325–1000 mg every 4–6 hrs	Max: 4,000 mg/day	14 15
CVD Prevention (primary/secondary)	75–100 mg daily (low-dose)	81 mg common; 325 mg sometimes used	1 5 9
Cancer Prevention	75–100 mg daily	Long-term; benefits after 5–10 years	1 2
Thromboprophylaxis	81–325 mg twice daily	Post-arthroplasty; 81 mg as effective	4 8 10
Preeclampsia Prevention	50–150 mg daily	Start ≤16 weeks gestation	6
AERD Management	325–650 mg twice daily	Titrate to lowest effective dose	7

Table 2: Common Aspirin Dosages by Indication

Low-Dose vs. Standard Dose

• Low-dose aspirin (75–100 mg daily) is most commonly used for cardiovascular and cancer prevention. Recent trials show no significant difference in efficacy or bleeding risk compared to 325 mg daily for secondary prevention, but patients are more likely to stick to the lower dose 9.
• For pain relief, much higher doses (325–1000 mg every 4–6 hours) are needed, but these are not suitable for long-term use due to increased risk of side effects 14.
• In post-surgical thromboprophylaxis, studies show 81 mg twice daily is as effective as 325 mg twice daily, with similar or slightly lower rates of bleeding and other complications 8 10.

Dosing for Special Populations

• Pregnancy: For preeclampsia prevention, 50–150 mg daily is recommended, ideally starting before 16 weeks of gestation. Higher doses within this range may confer greater benefit 6.
• AERD: Initial therapy often starts at 650 mg twice daily, then titrated down to 325 mg twice daily or lowest effective dose, balancing efficacy and side effects 7.

Duration of Therapy

• CVD/Cancer Prevention: Benefits accrue over years; commitment to daily long-term use is needed 1 2.
• Thromboprophylaxis: Typically 4–6 weeks post-surgery 4 8 10.
• Pain Management: Short-term use preferred due to gastrointestinal and bleeding risks 14.

Side Effects of Aspirin

While aspirin is often perceived as safe, especially at low doses, it carries real risks—some of which can be serious. The side effect profile depends on dose, duration, individual risk factors, and concurrent medications.

Side Effect	Description	Risk Factors	Source(s)
GI Bleeding/Ulcers	Stomach irritation, ulcers, bleeding	Age, higher dose, history of ulcers	13 14 15
Intracranial Bleeding	Hemorrhagic stroke, brain bleeds	Older age, hypertension	13 5 11 12
Hypersensitivity	Asthma, urticaria, anaphylaxis	Asthma, nasal polyps, chronic hives	15
Dyspepsia	Indigestion, stomach pain	Dose-dependent	7 14
Tinnitus	Ringing in ears (high doses)	Overdose, high-dose use	15
Ecchymosis/Bruising	Easy bruising	Elderly, concurrent anticoagulants	15

Table 3: Common and Serious Side Effects of Aspirin

Gastrointestinal Effects

Aspirin can damage the stomach lining, leading to gastritis, ulcers, and potentially serious gastrointestinal (GI) bleeding. The risk increases with higher doses, longer duration, older age, prior history of ulcers, and combining aspirin with other NSAIDs or certain drugs 13 14. Even low-dose aspirin increases GI bleeding risk by 59% over placebo in prevention trials 13.

Bleeding Risks

Aspirin’s antiplatelet action increases the risk of major bleeding elsewhere in the body, including the brain (intracranial bleeding, hemorrhagic stroke). The relative risk is about one-third higher than placebo, regardless of aspirin dose 13. Most extra bleeding events are non-fatal, but the risk must be weighed against potential cardiovascular benefit, especially in primary prevention 5 11 12 13.

Allergic and Hypersensitivity Reactions

Some individuals, especially those with asthma, nasal polyps, or chronic urticaria, may develop hypersensitivity reactions to aspirin—ranging from worsening asthma and hives to life-threatening anaphylaxis 15. This is known as aspirin-exacerbated respiratory disease (AERD), affecting up to 40% of people with both asthma and nasal polyps 15.

Other Side Effects

• Dyspepsia: Indigestion and stomach discomfort are common, especially at higher doses 7 14.
• Tinnitus: High doses can cause ringing in the ears, signaling potential toxicity 15.
• Bruising: Aspirin can cause easy bruising (ecchymosis), especially in older adults or those on other blood thinners 15.

Interactions of Aspirin

Aspirin’s beneficial and adverse effects can be amplified or diminished by other medications. Understanding these interactions is crucial for both patient safety and effectiveness.

Drug/Class	Interaction Outcome	Clinical Implication	Source(s)
NSAIDs (e.g., ibuprofen)	May reduce aspirin’s antiplatelet effect	Diminished CVD protection	16 18
Other NSAIDs (e.g., naproxen)	Additive GI/cardiac risk	Avoid combination	16 18
Anticoagulants (warfarin)	Increased bleeding risk	Monitor closely	13 15
SSRIs	Increased bleeding risk	Caution advised	13
Corticosteroids	Increased GI ulcer risk	GI protection may be needed	13
Acetaminophen	No major antiplatelet interaction	Safer for pain relief	16

Table 4: Notable Drug Interactions with Aspirin

NSAID Interactions

Many NSAIDs (like ibuprofen and naproxen) can interfere with aspirin’s antiplatelet effects, potentially reducing its cardiovascular protective benefits 16. This occurs at the level of the COX-1 enzyme. Some NSAIDs (e.g., diclofenac, ketorolac) do not interfere, but most common over-the-counter NSAIDs do 16. Combining NSAIDs with aspirin also increases the risk of GI bleeding and ulcers 18.

Anticoagulants and Antiplatelet Agents

Concurrent use of aspirin with other blood thinners (warfarin, clopidogrel, direct oral anticoagulants) significantly raises bleeding risks 13 15. For patients who must take both, close monitoring is essential.

Other Medications

• SSRIs: These antidepressants can increase bleeding risk when combined with aspirin 13.
• Corticosteroids: The risk of GI ulceration and bleeding is higher when aspirin is used with corticosteroids 13.
• Acetaminophen: Unlike NSAIDs, acetaminophen does not interfere with aspirin’s antiplatelet action and is often preferred for additional pain relief 16.

Special Considerations

• Multiple drugs and over-the-counter products can interact with aspirin. Always consult a healthcare provider before starting or stopping aspirin, especially if taking other medications or if you have chronic health issues.

Conclusion

Aspirin remains a foundational medication with proven benefits and well-characterized risks. Its optimal use depends on individual risk factors, health status, and thoughtful consideration of the evidence.

Key Takeaways:

• Versatile Uses: Aspirin is effective for pain, fever, cardiovascular and cancer prevention, clot prevention after surgery, preeclampsia prevention, and AERD management.
• Right Dose Matters: Most preventive uses require low-dose (75–100 mg daily); higher doses are reserved for acute pain or specific conditions like AERD.
• Real Risks: Gastrointestinal and intracranial bleeding are the main serious side effects, even at low doses. Hypersensitivity reactions can occur, especially in at-risk populations.
• Serious Interactions: NSAIDs (like ibuprofen) can reduce aspirin’s heart benefits; many drugs can increase bleeding risk—stay vigilant about drug combinations.
• Individualized Decisions: Aspirin’s benefits and risks must be carefully balanced, especially for primary prevention; discuss with your healthcare provider before starting or stopping aspirin.

Aspirin’s story reflects the evolution of medicine itself—anchored in tradition but continually refined by new evidence. Used thoughtfully, it can be life-saving; used indiscriminately, it can do harm. As always, informed and individualized care is the key to unlocking its full potential.