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Aspirin, or acetylsalicylic acid (ASA), is commonly used as a pain reliever for minor aches and pains and to reduce fever. It is also an anti-inflammatory drug and can be used as a blood thinner.

People with a high risk of blood clots, stroke, and heart attack can use aspirin long-term in low doses.

Aspirin contains salicylate, which derives from willow bark. Its use was first recorded around 400 BCE, in the time of Hippocrates, when people chewed willow bark to relieve inflammation and fever.

It is often given to patients immediately after a heart attack to prevent further clot formation and cardiac tissue death.

Fast facts on aspirin

Here are some key points about aspirin. More detail is in the main article.

  • Aspirin is one of the most widely used medications in the world.
  • It comes from salicylate, which can be found in plants such as willow trees and myrtle.
  • Aspirin was the first non-steroidal anti-inflammatory drug (NSAID) to be discovered.
  • It interacts with a number of other drugs, including warfarin and methotrexate.

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Aspirin has a range of uses, including the treatment of pain and inflammation and reduction of blood clotting.

Aspirin is a non-steroidal anti-inflammatory drug (NSAID).

NSAIDs are medications with the following effects:

  • Analgesic: Relieves pain without anesthesia or loss of consciousness
  • Antipyretic: Reduces a fever
  • Anti-inflammatory: Lowers inflammation when used in higher doses

Non-steroidal means they are not steroids. Steroids often have similar benefits, but they can have unwanted side effects.

As analgesics, NSAIDs tend to be non-narcotic. This means they do not cause insensibility or stupor. Aspirin was the first NSAID to be discovered.

Salicylate in the form of willow bark has been used for over 2,000 years. Some people still use willow bark as a more natural remedy for headaches and minor aches and pains.

Aspirin in its present form has been around for over 100 years. It is still one of the most widely used medications in the world. It is estimated that around 35,000 metric tons of aspirin is consumed annually.

Aspirin is a trademark owned by the German pharmaceutical company, Bayer. The generic term for aspirin is acetylsalicylic acid (ASA).

Aspirin is one of the most commonly used drugs for treating mild to moderate pain, migraines, and fever.

Common uses include headaches, period pains, colds and flu, sprains and strains, and long-term conditions, such as arthritis.

For mild to moderate pain, it is used alone. For moderate to severe pain, it is often used along with other opioid analgesic and NSAIDs.

In high doses, it can treat or help reduce symptoms of:

  • rheumatic fever
  • rheumatic arthritis
  • other inflammatory joint conditions
  • pericarditis

In low doses, it is used:

  • to prevent blood clots from forming and reduce the risk of a transient ischemic attack (TIA) and unstable angina
  • to prevent myocardial infarction in patients with cardiovascular disease by preventing clot formation
  • to prevent a stroke, but not to treat a stroke
  • to prevent colorectal cancer

Aspirin and children

Aspirin is not usually suitable for those aged under 16 years, because it can increase the risk of Reye's syndrome, which can appear after a virus, such as a cold, flu, or chicken pox. It can lead to permanent brain injury or death.

However, a specialist may prescribe aspirin for a child under supervision if they have Kawasaki disease, and to prevent blood clots from forming after heart surgery.

Acetaminophen (paracetamol, Tylenol) and ibuprofen are generally used instead.

Low-dose aspirin

A low dose of aspirin, at 75-81 milligrams (mg) per day, can be used as an antiplatelet medication, to prevent blood clots from forming.

This may be given to patients following:

  • a coronary artery bypass graft operation
  • a heart attack
  • a stroke
  • atrial fibrillation
  • acute coronary syndrome

People may also be given low-dose aspirin if they have the following risk factors, and if the doctor believes there is a chance of heart attack or stroke:

Others who may be advised to take low-dose aspirin include:

  • those with damage to the retina, or retinopathy
  • people who have had diabetes for over 10 years
  • patients who are taking antihypertensive medications

The United States (U.S.) Preventive Services Task Force currently recommend daily low-does aspirin use to prevent cardiovascular disease and colorectal cancer in adults aged 50 to 59 years who:

  • have a 10 percent or higher risk of cardiovascular disease
  • who do not have a high risk of bleeding
  • are likely to live at least another 10 years
  • are willing to take the dose for at least 10 years

In all these cases, the individual will normally continue to take low-dose aspirin daily for the rest of their life.

Aspirin is not recommended for individuals who:

  • have a peptic ulcer
  • hemophilia or any other bleeding disorder
  • a known allergy to aspirin
  • an allergy to any NSAID, such as ibuprofen
  • are at risk of gastrointestinal bleeding or hemorrhagic stroke
  • drink alcohol regularly
  • are undergoing dental or surgical treatment, however small

People with the following conditions should be cautious about taking aspirin, and should only do so if the doctor agrees:

  • asthma
  • uncontrolled hypertension
  • a previous peptic ulcer
  • liver problems
  • kidney problems

Aspirin is not given during a stroke, because not all strokes are caused by a clot. In some case, aspirin could make the stroke worse.

Anyone who is preparing to have a surgical operation should tell their doctor if they are taking regular aspirin. They may need to stop taking the aspirin at least 7 days before the operation.

Patients who are pregnant or breast-feeding may take low-dose aspirin, but only under a doctor's supervision. High-dose aspirin is not recommended.

Sometimes, one drug can make another medication less effective, or the combination can increase the risk to the patient. This is called a drug interaction.

The most common drugs that aspirin may interact with are:

  • Anti-inflammatory painkillers, such as diclofenac, ibuprofen, indomethacin, and naproxen. These can increase the risk of stomach bleeding if taken in combination with aspirin.
  • Methotrexate, used in the treatment of cancer and some autoimmune diseases. Aspirin can make it harder for the body to eliminate methotrexate, resulting in high and potentially dangerous levels of methotrexate in the body.
  • Selective serotonin reuptake inhibitors (SSRI) antidepressants, such as citalopram, fluoxetine, paroxetine, venlafaxine, and sertraline. Taken with aspirin, these can increase the risk of bleeding.
  • Warfarin, an anticoagulant drug, or a blood thinner, which stops the blood from clotting. If aspirin is taken with warfarin, it can reduce the drug's anticoagulant effects and increase the risk of bleeding. In some situations, however, a doctor may prescribe aspirin together with warfarin.

These are not the only drugs that cannot be used with aspirin. Anyone who is taking aspirin should inform their doctor, as other drugs can also interact.

The most common side effects of aspirin are:

The following adverse effects are possible, but less common:

  • worsening asthma symptoms
  • vomiting
  • inflammation of the stomach
  • stomach bleeding
  • bruising

An rare side effect of low-dose aspirin is hemorrhagic stroke.

Aspirin can help prevent and treat a range of conditions, but anyone who is taking aspirin should first speak to a doctor. Anyone under 16 years should not normally take aspirin, except in rare cases and under medical supervision.

There is a selection of aspirin available for purchase online.