Home Medicines Acetylsalicylic acid: effect, areas of application, side effects

Acetylsalicylic acid: effect, areas of application, side effects

by Josephine Andrews
Published: Last Updated on 416 views

Acetylsalicylic acid (ASA) is one of the most successful medicinal substances. It is used as a pain reliever, antipyretic, anti-inflammatory and as a blood platelet inhibitor to prevent blood clots (e.g. after a heart attack). The first drug with ASA as an active ingredient came onto the market in 1899. There are now numerous other preparations. Here you can read everything you need to know about acetylsalicylic acid.

This is how acetylsalicylic acid works

Acetylsalicylic acid (ASA) inhibits the formation of prostaglandins – tissue hormones that play an important role in inflammatory processes, pain mediation and fever . Thus, acetylsalicylic acid has an analgesic, antipyretic, anti-inflammatory and antirheumatic effect.

The inhibitory effect on the release of prostaglandins has another effect. Normally, prostaglandins promote blood clotting . By preventing the release of prostaglandins, acetylsalicylic acid also has an anticoagulant effect.

It also has “blood-thinning” properties. As a blood platelet inhibitor (thrombocyte aggregation inhibitor), ASA prevents the aggregation of the blood platelets – the blood remains thin so that blood clots cannot form so easily, which may then block a vessel in the heart or brain .

Acetylsalicylic acid is therefore suitable for preventing heart attacks and strokes in high-risk patients. For this area of ​​application, the required dosages are significantly lower than when ASA is given to reduce pain and fever.

intake, degradation and excretion

Orally taken acetylsalicylic acid is rapidly and almost completely absorbed into the blood from the stomach and small intestine . When it is processed in the body, the active substance salicylic acid in particular is formed .

While acetylsalicylic acid itself is broken down very quickly, the higher the dose of acetylsalicylic acid taken, the longer it takes to break down the resulting salicylic acid.

Salicylic acid is primarily excreted via the kidneys.

When is acetylsalicylic acid used?

The areas of application (indications) of the higher dose (500 to 3,000 milligrams per day) acetylsalicylic acid are:

Indications for low-dose (100 to 300 milligrams per day) acetylsalicylic acid are:

This is how acetylsalicylic acid is used

Acetylsalicylic acid is usually used orally, i.e. taken by mouth – usually in the form of tablets. The anticoagulant and blood-thinning effect develops even at low doses, while higher doses of acetylsalicylic acid are necessary for pain relief, fever reduction and anti-inflammatory effects.

ASA should not be taken on an empty stomach because it irritates the gastric mucosa and, in the worst case, can lead to gastrointestinal ulcers and bleeding. In addition, the medication should always be taken with a sufficient amount of liquid (e.g. a glass of water).

Acetylsalicylic acid and other painkillers should not be taken for more than three days in a row and no more than ten days per month without medical advice.

Combination preparations with acetylsalicylic acid

Acetylsalicylic acid is also available in combination with other active substances, resulting in an improved overall effect (e.g. blood thinning or pain relief). For example, there are blood-thinning combination preparations made from acetylsalicylic acid and another anticoagulant (clopidogrel, dipyridamole). Also available is the combination of ASA (to inhibit blood platelets), atorvastatin (to lower cholesterol) and ramipril (to treat high blood pressure and heart failure).

Painkillers containing acetylsalicylic acid, paracetamol and caffeine (used to treat tension headaches and mild migraines) are also available.

What are the side effects of acetylsalicylic acid?

Side effects of acetylsalicylic acid are mainly found in the gastrointestinal tract because the active ingredient can damage the mucous membrane. As a result, more than ten percent of all patients taking acetylsalicylic acid develop, for example, stomach pain or tiny bleeding (microbleeding) in the digestive tract.

In higher doses, nausea, vomiting, diarrhea , gastrointestinal ulcers, anemia due to iron deficiency (iron deficiency anemia) and   dizziness can also occur.

Between one and ten percent of users react to taking acetylsalicylic acid with nausea, vomiting and/or diarrhea.

In less than one percent of patients, acetylsalicylic acid causes, for example, disturbances in the acid-base balance, hearing disorders ( tinnitus ), visual disturbances , confusion, drowsiness (somnolence), allergic skin reactions and spasms in the muscles of the airways (bronchospasm).

Furthermore, changes in the blood count (such as a reduction in the number of white blood cells) and accumulation of water in the tissue (oedema) are possible. The latter can occur because more water and sodium ions are retained in the body.

In addition, acetylsalicylic acid can cause what is known as Reye’s syndrome – a rare, life-threatening disease of the brain and liver . It can occur primarily in children between the ages of four and nine who have a viral infection and receive ASA. How exactly this can lead to the development of Reye’s syndrome has not yet been clarified. It is also unknown how often Reye’s syndrome occurs in connection with the intake of acetylsalicylic acid.

Reye’s syndrome is the reason why acetylsalicylic acid can only be given to children under the age of twelve with a doctor’s prescription!

When not to take acetylsalicylic acid?


In certain cases, acetylsalicylic acid must not be used under any circumstances. These absolute contraindications include:

  • Gastrointestinal ulcers or bleeding
  • allergic reactions to salicylates

In addition, acetylsalicylic acid may only be given in many cases if a doctor considers the benefit of the application to be higher than the associated risks (such as gastrointestinal bleeding). These so-called relative contraindications include:

  • bronchial asthma
  • hearing loss (hypacusis)
  • Simultaneous use with other anticoagulant drugs (exception: low-dose heparin therapy)


Caution is advised when using acetylsalicylic acid in patients with nasal polyps , chronic inflammation of the nose and paranasal sinuses with polyp formation (chronic hyperplastic rhinosinusitis) or asthma. You may react to painkillers such as acetylsalicylic acid with an asthma attack (analgesic asthma).

With simultaneous use, acetylsalicylic acid can increase the effectiveness of the following medicinal substances:

  • Digoxin and Digitoxin (heart medicines)
  • Lithium (for manic-depressive disorders etc.)
  • Methotrexate (for rheumatism, cancer)
  • Triiodothyronine (for hypothyroidism , etc.)

In addition, acetylsalicylic acid can reduce the effect of the following substances:

  • spironolactone, canrenoate, loop diuretics (water pills)
  • high blood pressure medicines (antihypertensives)

age restriction

ASA preparations for self-medication may only be used from the age of twelve. With a doctor’s prescription, it can also be used under the age of 12.

pregnancy and breast feeding period

In the first and second trimester of pregnancy (1st and 2nd trimester), acetylsalicylic acid should not be taken unless the doctor deems it absolutely necessary and prescribes its use. In the last trimester of pregnancy, the active ingredient must not be taken under any circumstances.

An exception to this is the use of low-dose ASA (100 to 300 milligrams per day) under medical supervision. If indicated, this can be carried out throughout pregnancy.

Occasional use of acetylsalicylic acid is permitted during breast-feeding. In general, however, women should consult a doctor before using any medication while breastfeeding (as well as during pregnancy).

How to get medicines with the active ingredient acetylsalicylic acid

Preparations with acetylsalicylic acid do not require a prescription in Germany, Austria and Switzerland and are available in pharmacies. This does not apply to medicines that contain a prescription drug in addition to acetylsalicylic acid.

Since when is acetylsalicylic acid known?

Acetylsalicylic acid is a derivative of salicylic acid. This pain-relieving and fever-reducing active ingredient was first isolated from the herbaceous plant meadowsweet in 1835.

However, another plant acted as the namesake, the white willow – Salix alba in Latin . As early as 1829, the substance salicin, from which salicylic acid can be produced, was extracted from Salix extracts.

The pure salicylic acid burns the oral and gastric mucosa, which is why researchers have been looking for an alternative for a long time. It was discovered by the German chemist Felix Hoffmann. In 1897 he was the first to synthesize acetylsalicylic acid. He allowed the salicylic acid to react with an acetic acid derivative, resulting in the better tolerated acetylsalicylic acid. The first drug with this active ingredient finally came onto the market in 1899.

What else you should know about acetylsalicylic acid

The anticoagulant effect of acetylsalicylic acid and thus the increased tendency to bleed last for several days after stopping the drug. Therefore, acetylsalicylic acid must be discontinued in good time before an operation.

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