Acetylsalicylsäure – besser bekannt als ASS oder Aspirin – ist eines der ältesten und vielseitigsten Medikamente der Welt. In niedriger Dosierung (100 mg) schützt es Millionen Herz-Kreislauf-Patienten vor Herzinfarkt und Schlaganfall. In höherer Dosierung (500–1.000 mg) lindert es Schmerzen, Fieber und Entzündungen.
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This article is for informational purposes only and does not replace medical advice. Low-dose aspirin (75–100 mg) as long-term medication should never be started or stopped without consulting your doctor.
Acetylsalicylic acid (aspirin / ASA) is one of the oldest and most widely sold active substances in the world — and at the same time one of the most frequently misunderstood. Depending on the dose, it acts as a painkiller, fever reducer, or blood thinner. The overview below shows the most important pharmacological data.
| Property | Details |
|---|---|
| Active substance | Acetylsalicylic acid (ASA) |
| ATC code | B01AC06 (antiplatelet) / N02BA01 (analgesic) |
| Drug class | NSAID / antiplatelet agent |
| Available forms | Tablets (75 mg, 100 mg, 300 mg, 500 mg), dispersible tablets, chewable tablets, granules, i.v. solution |
| Half-life | ASA: approx. 15–20 min (rapidly converted to salicylic acid); salicylic acid: 2–3 hours |
| Duration of action on platelets | 7–11 days (lifespan of platelets) — irreversible! |
| Prescription status | Available over the counter as a painkiller; low-dose aspirin for long-term use should be medically supervised |
| Special feature | The only NSAID with irreversible platelet inhibition |
What many people don't realise: aspirin is not one medication but two — depending on the dose. At a high dose (500–1,000 mg) it acts as a painkiller and fever reducer. At a low dose (75–100 mg daily) it is a heart-protective medication that prevents platelets from clumping together. Both uses have different target groups, risks, and intake rules. Knowing both helps avoid dangerous mistakes.
| Aspirin as a painkiller | Aspirin as a blood thinner | |
|---|---|---|
| Dose | 500–1,000 mg per dose | 75–100 mg per day |
| Intake | As needed (max. 3,000 mg/day) | Daily as long-term medication |
| Effect | Pain relief, fever reduction, anti-inflammatory | Platelet aggregation inhibition |
| Target group | Headaches, migraine, toothache, fever | After heart attack, stroke, stent, coronary artery disease, peripheral arterial disease |
| Stomach risk | High with frequent use | Elevated; often combined with a PPI (pantoprazole) for stomach protection |
The most common mistake in practice: patients taking low-dose aspirin for blood thinning reach for an additional higher-dose aspirin tablet — or for ibuprofen — when they have a headache. Both can compromise the heart-protective effect or massively increase bleeding risk. More on this in chapter 6.
Aspirin inhibits the enzyme cyclooxygenase (COX) — similarly to ibuprofen and diclofenac. The crucial difference: aspirin inhibits COX irreversibly through acetylation. The enzyme is permanently switched off and cannot be repaired. This is why a single missed low-dose aspirin barely matters — but also why its effect only fully wears off 7–11 days after stopping.
At low doses, aspirin primarily inhibits COX-1 in the platelets. This reduces the production of thromboxane A2 — a substance that normally causes platelets to clump together. Since platelets have no cell nucleus, they cannot reproduce the destroyed enzyme. The effect therefore lasts for as long as the platelet lives: 7–11 days.
At higher doses, aspirin additionally inhibits COX-2 in various tissues. This reduces prostaglandins responsible for pain, fever, and inflammation — but also those that maintain the protective stomach lining. This explains the stomach side effects.
The correct dose of aspirin depends entirely on the treatment goal. Confusing the dose levels can be dangerous — too high a dose increases bleeding risk, too low a dose does not provide adequate pain relief. Record your aspirin dose in your digital medication plan.
| Indication | Dose | Intake | Max. duration without doctor |
|---|---|---|---|
| Heart protection / blood thinning | 75–100 mg/day | Once daily, long-term | Only with medical prescription |
| After stent (dual antiplatelet therapy) | 75–100 mg/day + clopidogrel/ticagrelor | Daily, 6–12 months | Strictly as medically directed |
| Acute heart attack (first aid) | 300 mg | Single dose, chewed (!) | Emergency |
| Pain / fever (adults) | 500–1,000 mg | Every 4–6h, max. 3,000 mg/day | Max. 3–4 days |
| Migraine (guideline recommendation) | 900–1,000 mg | Single dose during attack | – |
The main risk of aspirin lies in the gastrointestinal tract and increased bleeding tendency. Both risks exist even with the low 75–100 mg dose and should not be underestimated — especially in patients over 65 or those taking other blood-thinning medications. Systematically documenting side effects enables early intervention.
Aspirin inhibits the formation of protective prostaglandins in the stomach lining. This increases the risk of gastric ulcers and gastrointestinal bleeding. Enteric-coated aspirin reduces local stomach irritation but does not prevent the systemic effect on the stomach lining. For patients at risk, a PPI such as pantoprazole or omeprazole for stomach protection is advisable.
| Side effect | Frequency | What to do |
|---|---|---|
| Stomach pain / heartburn | Common | Always take after a meal. Consider a PPI for stomach protection |
| Gastrointestinal bleeding | Occasional | Black stools = emergency! See a doctor immediately |
| Increased bleeding tendency | Common | Bruising more easily, longer bleeding from cuts |
| Nosebleeds, bleeding gums | Common | Inform your doctor if frequent |
| Aspirin-induced asthma (ASA intolerance) | Rare (but: 10–20% of asthmatics!) | Aspirin contraindicated! Alternative: clopidogrel |
| Allergic reactions | Rare | Difficulty breathing, skin rash → call 999 |
| Reye's syndrome (children!) | Very rare, potentially fatal | Aspirin contraindicated in under-16s (exception: Kawasaki disease) |
Particularly important: black stools are a warning sign of a gastrointestinal bleed and a medical emergency. Anyone on long-term aspirin therapy who notices unusual abdominal pain or changes in stool should see a doctor immediately.
This is the most dangerous and at the same time most commonly overlooked interaction in patients on long-term aspirin therapy. Many reflexively reach for ibuprofen for back pain, headaches, or joint pain — not knowing they are jeopardising their heart protection. brite's interaction check detects this combination automatically.
| Scenario | Blood-thinning effect preserved? | Recommendation |
|---|---|---|
| Aspirin 75–100 mg in morning, ibuprofen 4+ hours later | Yes — aspirin has already bound irreversibly | Possible solution for occasional need |
| Ibuprofen first, aspirin later | No — ibuprofen blocks the binding site | Dangerous: heart protection cancelled! |
| Ibuprofen and aspirin at the same time | No — ibuprofen "wins the race" | Avoid! |
| Paracetamol (acetaminophen) instead of ibuprofen | Yes — does not interfere with aspirin's effect | Best alternative for patients on long-term aspirin |
Beyond the ibuprofen trap, there are further clinically relevant interactions — especially for patients on long-term blood thinners or stomach medication. Check your combination with the interaction check.
| Substance / medication | Interaction | Recommendation |
|---|---|---|
| Warfarin / phenprocoumon | Massively increased bleeding risk | Only with strict medical supervision; close INR monitoring |
| DOACs (apixaban, rivaroxaban) | Increased bleeding risk | Avoid triple therapy; stop aspirin as early as possible after stent |
| Corticosteroids (prednisolone) | Greatly increased risk of gastrointestinal bleeding | Always add a PPI (stomach protection) |
| Methotrexate | Aspirin reduces methotrexate excretion → toxicity | Avoid combination or monitor closely |
| SSRIs (citalopram, sertralin) | SSRIs additionally increase bleeding risk | PPI stomach protection recommended |
| Alcohol | Greatly increased risk of gastrointestinal bleeding | Minimise alcohol during long-term aspirin therapy |
| Ramipril / ACE inhibitors | Aspirin can slightly reduce the effect of ACE inhibitors | Usually not clinically significant at 75–100 mg |
Particularly for patients on anticoagulant therapy: the combination aspirin + warfarin or aspirin + DOAC requires close medical monitoring. Bleeding risks are cumulative — and minor injuries can lead to serious complications. Use the medication list to keep track of all combinations.
