What is the difference between aspirin, acetaminophen, and ibuprofen? 

This week learn about the difference between common over the counter pain relievers
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Standing in the pain relief aisle of the pharmacy, you may have wondered how there came to be so many different brands offering so many different types of pain relief. Pain relievers, or analgesics, are sorted into three main categories. The largest category are the non-steroidal anti-inflammatory drugs, or NSAIDs, including aspirin, ibuprofen, and naproxen. These drugs reduce pain, inflammation, and fever, but as the name suggests, are not steroids, which have a very specific chemical structure. Acetaminophen, or paracetamol as it is known internationally, has no anti-inflammatory properties and therefore is not considered an NSAID. Finally, opioids, including codeine, morphine, and oxycodone, are very potent pain relievers with a high risk of addiction, and are therefore not available over the counter in the United States. Codeine, a relatively weak opioid, is available over the counter in some countries, generally in very small doses and combined with other pain relievers.
Aspirin, or acetylsalicylic acid, is the oldest of the modern over-the-counter pain relievers. It was developed in 1897 by chemists at Bayer, which is still one of the world’s leading producers of aspirin. Aspirin was developed as a safer alternative to salicylic acid, which in turn was isolated from the willow tree, a plant known for its pain relieving properties as early as ancient Sumer. While aspirin has been in widespread use since the early 1900s, it wasn’t until 1971 that Sir John Vane discovered how aspirin reduces pain, inflammation, and fever. Like all NSAIDs, aspirin works by stopping the two cyclooxygenase enzymes, COX-1 and COX-2 from producing prostaglandins. Prostaglandins are a group of several different hormones found throughout the body, which cause inflammation, pain, and fever as a natural response to injury or infection. Prostaglandins also play a role in regulating the female reproductive system and protecting the gastrointestinal tract, so while NSAIDs reduce pain, inflammation, and fever, they may also affect the menstrual cycle and cause stomach irritation and ulcers. Aspirin is unique in that it also stops the production of thromboxane, a substance which promotes blood clotting. Therefore, aspirin is the only NSAID that, taken regularly in low doses, can reduce the risk of a blood clot causing a heart attack or stroke. Aspirin is also the only NSAID that has been linked to Reye’s Syndrome, a serious liver disease that may occur in children during or after an infection. Therefore aspirin, and other salicylates like the antacid Pepto-Bismol and the oral treatment Bonjela, should not be given to children during a viral infection like the flu or chickenpox.
In an effort to find a safer alternative to aspirin, chemists began to develop other NSAIDs in the 1960s. The first and most popular of these was ibuprofen, first available over-the-counter in the early 1980s and currently marketed as Advil or Motrin in the United States. Another popular NSAID is naproxen, available over the counter as Aleve in the United States since the early 1990s. Different NSAIDs affect the two COX enzymes to differing degrees, and it is thought that those which target primarily the COX-2 enzyme have a lower risk of causing gastrointestinal bleeding and ulcers. Unfortunately, while non-aspirin NSAIDs are safe for children and gentler on the stomach than aspirin, they also carry an increased risk of heart attack and stroke.
Acetaminophen, the only modern non-NSAID pain reliever widely available over the counter, was first synthesized in the late 1800s. However, this discovery was largely ignored until two other non-NSAID pain relievers, phenacetin and acetanilide, were shown to have lethal side effects. In the search for a non-toxic alternative, Bernard Brodie and Julius Axelrod discovered that both phenacetin and acetanilide were changed into acetaminophen and other more dangerous compounds within the human body, but that acetaminophen by itself had no toxic properties. Acetaminophen was shown to be an effective pain reliever and fever reducer, and was marketed as Tylenol in the mid 1950s. The primary selling points of acetaminophen are that it carries no risk of causing gastrointestinal bleeding or ulcers, unlike NSAIDs, and that it is safe for children, unlike aspirin. However, acetaminophen has no anti-inflammatory properties, and a relatively small overdose can cause severe liver damage. It is not yet fully understood why acetaminophen works to relieve pain and reduce fever, but it is thought to interact with the COX enzymes in a manner that is more complicated than the NSAID pain relievers.