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Written by Healthwords's team of doctors and pharmacists based in UK | Updated: 01.03.2023 | 3 min read

Aspirin is an anti-inflammatory painkiller and antiplatelet. It tends to come in two different strengths: 300mg and 75mg (also known as baby aspirin). The 300mg dose is primarily used as a pain reliever, and the 75mg is used as an antiplatelet to help prevent blood clots forming in the body.

Aspirin can come in many different formulations, including dispersible, gastro-resistant and regular tablets. When taken as a tablet, it is important that is taken with or after food as it can cause stomach irritation. It is also formulated as oral gels, heat rub-on gels and heat sprays. It can start to work within 20 to 30 minutes of taking it, or instantly with rub or spray-on formulations.

Who is it for?

There are two key uses for aspirin: an anti-inflammatory painkiller and an antiplatelet, which is given to prevent cardiovascular events. If your doctor has suggested you are at a high risk of cardiovascular events, they may prescribe you 75mg daily. Don’t start taking it without speaking to your doctor though, as all medications carry possible risks as well as benefits.

Aspirin as a pain reliever is suitable for people who have tried paracetamol and are still in some pain. It can be a good next step in the treatment of musculoskeletal conditions such as sprains and strains. Taking aspirin gives more relief than paracetamol alone. Aspirin is also effective for toothache which is why there is aspirin-based oral gel available.

How does it work?

Aspirin is a non-steroidal anti-inflammatory drug (NSAID) from the same family as ibuprofen and naproxen. Because of this, make sure you aren’t taking aspirin alongside other anti-inflammatories, as this can upset your stomach.

Aspirin’s anti-inflammatory effect works by blocking the body’s production of chemicals called prostaglandins, which are released in response to illness or injury. Prostaglandins can cause pain and inflammation to alert the body that it is unwell. By stopping prostaglandin production, this medication can stop pain, inflammation and also fever.

Aspirin’s antiplatelet effect works by stopping platelets bunching together and therefore stops the blood from forming clots as easily.

You can take a dose of aspirin every 4-6 hours if needed but you should not take more than 4g in 24 hours.

Should anyone avoid taking aspirin?

Like all medications, avoid aspirin if you have previously had an allergic reaction to the medication, if you have severe kidney or liver problems, or if you have other medications or medical conditions where you would normally discuss with your doctor or pharmacist before starting something new.

Nobody under the age of 16 should take aspirin due to an adverse reaction called Reyes syndrome, which can be very serious.

If you are asthmatic and haven’t had anti-inflammatories before, they can sometimes cause an acute asthma attack.

You should avoid aspirin if you are trying to get pregnant or are already pregnant, unless advised by your midwife or doctor. If you have a known stomach ulcer, or inflammatory bowel disease, you should avoid taking aspirin unless recommended by your doctor.

Are there any side effects?

Common side effects include headaches, feeling dizzy, nausea and vomiting. This is often because excess amounts of aspirin in the brain can bind to other receptors causing undesired effects. In this case, you may wish to try a lower dose.

Indigestion and heartburn are other common side effects of all anti-inflammatories, as they can irritate the lining of the stomach. If they are taken in the long-term without any stomach protection medication, they can cause stomach ulcers.

If you have started aspirin and your doctor doesn’t know, you should speak to them to see if they would recommend stomach protection medication when taking aspirin.

As with any medication, seek urgent medical advice if any symptoms develop of an allergic reaction such as a skin rash, shortness of breath, wheezing, or swelling of the tongue, mouth, lips, face or throat.

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