Aspirin

Pronunciation: AS-pir-in.

Last medically reviewed: August 14, 2026, by , MBBS, MD (Internal Medicine).

Generic name
acetylsalicylic acid
Drug class
Nonsteroidal anti-inflammatory drug (NSAID) and antiplatelet agent (salicylate)
Form
Tablet, chewable tablet, gastro-resistant (enteric-coated) tablet, dispersible tablet
Route
Oral
Legal status
Over-the-counter (general sale/pharmacy) in most markets; low-dose antiplatelet use is usually clinician-recommended

Availability and supply rules vary by country

Trade names by country: United States · United Kingdom · Canada · Australia · New Zealand

Australia: Various ARTG-registered aspirin products (e.g. Pharmacy Health Low Dose Aspirin, Mayne Pharma Aspirin 100) (5) · Full directory

What acetylsalicylic acid is and how it works

Aspirin is a widely used over-the-counter medicine that relieves pain, reduces fever, and reduces inflammation at standard doses, and helps prevent blood clots at low doses. It belongs to the NSAID and salicylate family of medicines. (2) (4)

Aspirin is used very differently depending on the dose: a low daily dose (usually 75-150 mg) is used long-term, often on a doctor's advice, to help prevent heart attack or stroke by reducing blood clotting, while a higher dose (as directed on the product label or by a doctor) is used short-term for pain, fever, or inflammation. Follow the product label or your prescriber's instructions for your specific use.

Mechanism of action: how acetylsalicylic acid works

Aspirin (acetylsalicylic acid) irreversibly inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis (producing analgesic, antipyretic, and anti-inflammatory effects at higher doses) and irreversibly inhibiting platelet thromboxane A2 production (producing an antiplatelet effect at low doses that lasts the lifetime of the affected platelets, about 7-10 days). (2) (4)

What acetylsalicylic acid is used for

Pain, fever, and inflammation relief (standard dose)

Used for temporary relief of minor aches and pains, headache, muscle aches, backache, menstrual cramps, dental pain, and to reduce fever, typically at doses of 325-650 mg as needed, following label directions. (1) (4)

Secondary prevention of heart attack and stroke (low dose)

Used at a low daily dose (usually 75-150 mg once daily) for secondary prevention of thrombotic cardiovascular or cerebrovascular disease, including after a previous heart attack, stroke, or coronary artery bypass surgery, as directed by a prescriber. (2)

Before taking acetylsalicylic acid

Do not take / not appropriate for

  • Do not take aspirin if you have a known allergy or hypersensitivity to aspirin, other salicylates, or other NSAIDs (including allergic reactions such as asthma, hives, or facial swelling triggered by these medicines). (all countries) (1) (2) (4)
  • Do not take aspirin if you have an active stomach or duodenal ulcer, active gastrointestinal bleeding, or a bleeding disorder. (all countries) (2) (4)
  • Do not give aspirin to children or teenagers under 18 with chickenpox, flu, or other viral illness symptoms without first consulting a doctor or pharmacist, because of the risk of Reye's syndrome, a rare but serious illness. (all countries) (1) (2) (4) (5) (6)
  • Avoid aspirin doses above 100 mg/day during the third trimester of pregnancy unless specifically directed by a doctor, because of risks to the unborn baby. (United Kingdom, United States, Canada) (1) (2) (4)

Tell your clinician about

  • Any history of stomach ulcers, gastrointestinal bleeding, or bleeding disorders.
  • Asthma, especially if it has ever been triggered by aspirin or other NSAIDs.
  • High blood pressure, heart disease, liver disease, or kidney disease.
  • All other medicines you take, including anticoagulants (blood thinners), other NSAIDs, methotrexate, and diuretics.
  • If you drink 3 or more alcoholic drinks daily.
  • If you are pregnant, trying to become pregnant, or breastfeeding.
  • If you have surgery or dental work planned in the next 5-7 days.
  • If you are 60 years of age or older, because of increased risk of stomach bleeding.
(1) (2) (4)

How to take acetylsalicylic acid

  • Take with a full glass of water or milk to help reduce stomach upset.
  • Follow the exact dose and frequency on the product label, or as directed by your prescriber -- do not exceed the labeled maximum daily amount.
  • Chewable tablets should be chewed or crushed completely before swallowing; gastro-resistant (enteric-coated) tablets should be swallowed whole, not crushed or chewed.
  • Low-dose aspirin for heart/stroke prevention is usually taken once daily at a consistent time, as directed by a prescriber.
(1) (2) (4)

Procedures and treatment changes

Tell the treating team before surgery, procedures, or any medicine change. Do not alter treatment without the responsible clinician. (1) (2) (3) (4) (5) (6)

Missed dose

If you are taking daily low-dose aspirin as directed by a prescriber and miss a dose, contact your prescriber or pharmacist for guidance specific to your situation, rather than doubling a later dose. For occasional as-needed use, simply take the next dose when needed, following label directions.

Overdose

Aspirin overdose can be serious. Get medical help or contact a Poison Control Center right away if you think too much aspirin has been taken, including in a child, even if there are no symptoms yet. (1) (4)

Side effects

Side effects and their urgency vary; report severe, persistent, or concerning symptoms.

Stomach upset, indigestion, or heartburn.

What to notice: Stomach upset, indigestion, or heartburn.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Increased tendency to bleed or bruise.

What to notice: Increased tendency to bleed or bruise.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (2)

Nausea.

What to notice: Nausea.

What to do: Discuss persistent or troublesome symptoms with the treating clinician or pharmacist. (1)

Serious warnings

Reye's syndrome (children and teenagers with a viral illness) — high caution

Symptoms: Behaviour changes, confusion, unusual sleepiness, or persistent vomiting in a child or teenager who has or is recovering from chickenpox, flu, or another viral illness.

Action: Do not give aspirin to a child or teenager with chickenpox or flu-like symptoms without first checking with a doctor or pharmacist. If these symptoms occur after aspirin use, seek medical attention promptly -- this can be an early sign of Reye's syndrome, a rare but serious and potentially fatal illness. (1) (2) (4)

Signs of stomach or intestinal bleeding — emergency

Symptoms: Vomiting blood or material that looks like coffee grounds, black or bloody stools, or severe stomach pain that does not improve.

Action: Seek emergency medical help immediately. (1) (4)

Signs of a serious allergic reaction — emergency

Symptoms: Hives, facial or throat swelling, difficulty breathing, wheezing, or shock.

Action: Seek emergency medical help immediately. (1)

Ringing in the ears or hearing loss — high caution

Symptoms: Tinnitus (ringing in the ears) or reduced hearing.

Action: Contact a doctor -- this can be a sign that the dose needs review. (1)

Interactions

  • Anticoagulant ('blood-thinning') medicines such as warfarin -- increased risk of bleeding. (2) (4)
  • Other NSAIDs (such as ibuprofen or naproxen) -- increased risk of stomach ulceration and bleeding. (2) (4)
  • SSRIs (a type of antidepressant) -- increased risk of gastrointestinal bleeding. (2)
  • Methotrexate -- aspirin can increase methotrexate levels and toxicity risk, especially at higher methotrexate doses. (4)
  • Alcohol -- drinking 3 or more alcoholic beverages daily increases the risk of stomach bleeding while taking aspirin. (1) (4)

Pregnancy, breastfeeding, kidney/liver function, age

Pregnancy

Avoid aspirin doses above 100 mg/day (or as specified on the product label) during the third trimester of pregnancy unless a doctor has specifically directed otherwise, because of risks including premature closure of a blood vessel in the baby's heart (ductus arteriosus) and effects on kidney function. Discuss any aspirin use in pregnancy with a prescriber. (1) (2) (3) (4) (5) (6)

Breastfeeding

Discuss aspirin use with a doctor or pharmacist before use while breastfeeding. (1) (2) (3) (4) (5) (6)

Children

Standard-dose aspirin is generally not recommended for children or teenagers with a current or recent viral illness (such as chickenpox or flu) because of the risk of Reye's syndrome; use in children should only follow specific medical advice. (1) (2) (3) (4) (5) (6)

Elderly

People aged 60 and older have an increased risk of stomach bleeding with aspirin and should use it cautiously, following label directions or a prescriber's advice. (1) (2) (3) (4) (5) (6)

Hepatic_impairment

Aspirin is contraindicated in severe liver impairment; discuss any liver condition with a prescriber before use. (1) (2) (3) (4) (5) (6)

Renal_impairment

Aspirin is contraindicated in severe kidney impairment; discuss any kidney condition with a prescriber before use. (1) (2) (3) (4) (5) (6)

Source_ids

US-DAILYMED-ASPIRIN-LOWDOSE-2026,UK-EMC-ASPIRIN-75MG-2026,CA-HC-ASPIRIN-LABELLING-STANDARD-2026 (1) (2) (3) (4) (5) (6)

Monitoring

Before starting

  • Review of bleeding risk factors and current medicines, including other NSAIDs and anticoagulants
  • Assessment of stomach ulcer or GI bleeding history

During treatment

  • Watching for signs of stomach bleeding, especially with long-term use.
  • Periodic review of ongoing need for low-dose antiplatelet therapy with a prescriber.
  • Monitoring for hearing changes (tinnitus) which can indicate a dose issue.
(2) (1)

Storage

Store at room temperature, protected from moisture. Keep out of reach of children -- aspirin overdose in children can be serious.

Study the drug class: Antiplatelet agents

Professional information

Clinician-facing context only, sourced from the current US FDA OTC labeling and UK SmPC; verify against the current full label before recommending.

United Kingdom

Indication: Secondary prevention of thrombotic cardiovascular/cerebrovascular disease

Dose summary: 75-150 mg once daily long-term; up to 300 mg daily short-term on medical advice in some circumstances. Contraindicated in active peptic ulceration, bleeding disorders, severe hepatic/renal impairment, and doses above 100 mg/day in the third trimester of pregnancy.

Renal context: Contraindicated in severe renal impairment per the UK SmPC. (2)

Canada

Indication: OTC analgesic/antipyretic use

Dose summary: 325/500 mg: 1-2 tablets every 4-6 hours, max 4000 mg/24h. 650 mg: 1 tablet every 4-6 hours, max 4000 mg/24h. Contraindicated with concurrent high-dose methotrexate (>=15 mg/week), active liver/kidney disease, and salicylate-sensitive asthma.

Renal context: Contraindicated in active kidney disease per Health Canada's labelling standard. (4)

Mechanism of action

Hepatic guidance

Contraindicated in severe hepatic impairment; use with caution and clinician oversight in milder impairment.

Overdose note

Aspirin overdose can cause tinnitus, hyperventilation, acid-base disturbance, and in severe cases, life-threatening metabolic derangement; management requires urgent medical assessment and is not a self-directed process. (2) (4)

Frequently asked questions

Is aspirin available in the US, UK, Europe, Canada, Australia, and New Zealand?

Yes, aspirin is available in all of these regions, both as a standard-dose over-the-counter pain/fever reliever and as a low-dose product used for cardiovascular protection. (1) (2) (3) (4) (5) (6)

What is Reye's syndrome and why does it matter for aspirin?

Reye's syndrome is a rare but serious illness that has been linked to aspirin use in children and teenagers recovering from a viral illness, especially flu or chickenpox. Because of this, aspirin should not be given to children or teenagers with these illnesses without first checking with a doctor or pharmacist. (1) (2) (4)

What is the difference between low-dose and regular-dose aspirin?

Low-dose aspirin (usually 75-150 mg once daily) is typically used long-term, often on a doctor's advice, to help prevent blood clots, heart attack, or stroke. Regular-dose aspirin (325-650 mg as needed, per label directions) is used short-term for pain, fever, or inflammation. The two uses are not interchangeable without medical guidance. (2) (4)

What is the mechanism of action of acetylsalicylic acid?

Aspirin (acetylsalicylic acid) irreversibly inhibits cyclooxygenase (COX-1 and COX-2) enzymes, reducing prostaglandin synthesis (producing analgesic, antipyretic, and anti-inflammatory effects at higher doses) and irreversibly inhibiting platelet thromboxane A2 production (producing an antiplatelet effect at low doses that lasts the lifetime of the affected platelets, about 7-10 days). (2) (4)

What is the generic name of Aspirin?

The generic name is acetylsalicylic acid. (1) (2)

What class of drug is acetylsalicylic acid?

Aspirin is classed as: Nonsteroidal anti-inflammatory drug (NSAID) and antiplatelet agent (salicylate). (1) (2)

References

  1. ASPIRIN LOW DOSE - aspirin tablet, chewable (Drug Facts label)U.S. Food and Drug Administration / DailyMed (NIH), OTC Drug Facts label · United States · accessed 2026-07-30 · source 1
  2. Aspirin 75mg Gastro-Resistant Tablets -- Summary of Product Characteristicselectronic medicines compendium (emc), United Kingdom · United Kingdom · accessed 2026-07-30 · source 2
  3. Acetylsalicylic acid -- list of nationally authorised medicinal products (PSUSA/00000039/202202)European Medicines Agency (EMA) -- list of nationally authorised medicinal products (PSUSA procedure) · European Union · accessed 2026-07-30 · source 3
  4. Guidance Document -- Acetylsalicylic Acid Labelling StandardHealth Canada -- Nonprescription Drugs Labelling Standard for Acetylsalicylic Acid (ASA) · Canada · accessed 2026-07-30 · source 4
  5. Aspirin products -- ARTG registrations (e.g. Pharmacy Health Low Dose Aspirin 100 mg, Mayne Pharma Aspirin 100)Therapeutic Goods Administration (TGA), Australia · Australia · accessed 2026-07-30 · source 5
  6. Changes to the Label Statements Database for aspirin (harmonisation with Australia)Medsafe (New Zealand regulator) -- Label Statements Database consultation outcome · New Zealand · accessed 2026-07-30 · source 6

Brand names by country

Single-ingredient acetylsalicylic acid names are shown separately by country. Product availability, strengths, and supply rules can change; combination products are not included here.

Priority countries

United States

  • Aspirin / Bayer Aspirin (various OTC brands, e.g. Aspirin Low Dose) (1)FDA OTC monograph and NDA products confirmed · 81 mg (low dose), 325 mg, 500 mg · Multiple OTC manufacturers under the FDA OTC monograph; select Rx low-dose products under individual NDAs

United Kingdom

  • Aspirin 75mg Gastro-Resistant Tablets / Nu-Seals (2)MHRA licensed emc smpc confirmed · 75 mg, 300 mg · Multiple UK-licensed manufacturers

Canada

  • ASA
  • ENTERIC COATED ASA
  • ENTROPHEN
  • ENTROPHEN ECT
  • ASPIRIN
  • ASA SUPPOSITORIES
  • ASPIRIN COATED
  • NOVASEN
  • ENTERIC COATED A.S.A
  • LOWPRIN

Australia

  • Various ARTG-registered aspirin products (e.g. Pharmacy Health Low Dose Aspirin, Mayne Pharma Aspirin 100) (5)TGA ARTG registered confirmed · 100 mg (low dose), 300-325 mg · Multiple sponsors including Mayne Pharma

New Zealand

  • Cartia, Aspec, Heartcare Aspirin, Cardiprin (6)Medsafe marketed confirmed · 75 mg, 100 mg, 150 mg · Multiple, including Aspen New Zealand (Cartia)
View brands in additional countries.

European Union

Aspirin (nationally authorised across EU member states, no single centralised EU brand) (3)

This page provides general reference information about aspirin and is not a substitute for advice from a doctor or pharmacist. Always follow the product label or your prescriber's instructions for your specific use.

Last medically reviewed: August 14, 2026, by , MBBS, MD (Internal Medicine). See the medical review policy.

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