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What are the side effects of paracetamol?

4 min read

Paracetamol is the most commonly used medication for pain and fever in the United States and Europe [1.7.3]. While generally safe at recommended doses, it's important to understand: what are the side effects of paracetamol?

Quick Summary

Paracetamol is well-tolerated, but side effects can occur. They range from rare allergic reactions to severe liver damage from overdose. Long-term use carries potential risks.

Key Points

  • Rarity of Side Effects: Side effects from paracetamol are rare when taken at the recommended dose, but can include allergic reactions and blood disorders [1.2.2].

  • Liver Damage Risk: The most serious side effect is severe liver damage (hepatotoxicity), which occurs from taking more than the recommended maximum daily dose [1.2.3, 1.7.3].

  • Overdose Symptoms: Early overdose symptoms may be mild or absent, but it is a medical emergency requiring immediate attention to prevent irreversible liver damage [1.3.2, 1.4.4].

  • Long-Term Use: Observational studies suggest long-term, high-dose use may be linked to an increased risk of cardiovascular, gastrointestinal, and renal adverse effects [1.7.3].

  • Special Populations: Individuals with liver or kidney problems, or those who consume alcohol regularly, should be particularly cautious with paracetamol use [1.6.2].

  • Pregnancy Safety: Paracetamol is considered the first-choice painkiller for use during pregnancy and breastfeeding [1.10.1].

  • Drug Interactions: Paracetamol can interact with other medications, notably increasing the anticoagulant effect of warfarin and the risk of liver toxicity with other drugs [1.9.2, 1.9.3].

In This Article

Understanding Paracetamol (Acetaminophen)

Paracetamol, also known as acetaminophen, is one of the most widely used over-the-counter medications for relieving mild to moderate pain and reducing fever [1.7.3]. It's found in hundreds of products, from standalone pain relievers to combination cold and flu remedies [1.8.2]. Because of its widespread availability, it's crucial to understand its potential side effects and the importance of using it correctly. While paracetamol is considered safe when taken at the recommended dose, adverse effects can and do occur, particularly with misuse or overdose [1.6.5, 1.2.2]. In the United States, acetaminophen toxicity is a leading cause of acute liver failure [1.8.4].

Common and Uncommon Side Effects

When taken as directed, side effects from paracetamol are rare [1.2.2]. Most people tolerate it well without any issues [1.6.5]. However, some individuals may experience adverse reactions.

Common Side Effects

Though infrequent, some of the more commonly reported adverse reactions, especially with the intravenous (IV) form, include:

  • Nausea and vomiting [1.2.1]
  • Constipation [1.2.1]
  • Injection site pain (for IV administration) [1.2.1]
  • Headaches [1.11.1]

Rare But Serious Side Effects

More severe side effects are rare but require immediate medical attention [1.2.1, 1.2.5]. These can be signs of a serious underlying issue or allergic reaction.

  • Allergic Reactions Symptoms of an allergic reaction include skin rash, hives, itching, and swelling, particularly of the face, tongue, or throat [1.4.4]. In very rare cases, a severe allergic reaction known as anaphylaxis can occur, causing difficulty breathing and a rapid heartbeat [1.4.2].
  • Severe Skin Reactions Extremely rare but potentially fatal skin reactions like Stevens-Johnson syndrome (SJS) and toxic epidermal necrolysis (TEN) have been associated with paracetamol [1.2.1, 1.7.3]. These conditions cause the top layer of skin to blister and peel.
  • Blood Disorders In very rare instances, paracetamol can lead to blood disorders such as thrombocytopenia (low platelet count), leukopenia (low white blood cell count), and neutropenia (low count of a specific type of white blood cell) [1.2.1, 1.6.3]. This can result in unusual bruising, bleeding, or getting more infections than usual [1.4.4].
  • Kidney Damage While the primary concern is liver damage, high doses or prolonged use may also strain the kidneys and potentially lead to complications or impairment [1.2.5, 1.7.3].

The Foremost Risk: Overdose and Liver Damage

The most significant risk associated with paracetamol is hepatotoxicity, or severe liver damage, from taking too much [1.2.3]. Paracetamol overdose is the leading cause of acute liver failure in the Western world [1.7.3]. This damage occurs because the liver's regular metabolic pathways become overwhelmed, leading to the production of a toxic byproduct called NAPQI [1.9.4]. The body's natural antioxidant, glutathione, which neutralizes NAPQI, gets depleted, allowing the toxin to damage liver cells [1.7.3, 1.11.3].

Symptoms of a paracetamol overdose develop in stages [1.3.2]:

  1. Stage 1 (first 24 hours): May include nausea, vomiting, sweating, and loss of appetite. Often, there are no symptoms at all [1.3.2, 1.4.4].
  2. Stage 2 (24 to 72 hours): Abdominal pain, particularly in the upper right quadrant where the liver is located, may develop [1.3.1, 1.3.2].
  3. Stage 3 (3 to 4 days): Symptoms worsen with the onset of liver failure, which can include jaundice (yellowing of the skin and eyes), confusion, and bleeding problems [1.3.2, 1.3.3].
  4. Stage 4 (after 5 days): The outcome is either recovery or fatal liver failure [1.3.2].

It is critical to seek immediate medical help if an overdose is suspected, even if the person feels well. Treatment with an antidote called N-acetylcysteine (NAC) is most effective when given within eight hours of the overdose [1.3.5].

Paracetamol vs. Ibuprofen: A Side Effect Comparison

Paracetamol and ibuprofen are both common choices for pain and fever, but they belong to different drug classes and have different side effect profiles.

Feature Paracetamol (Acetaminophen) Ibuprofen (NSAID)
Primary Mechanism Acts primarily in the central nervous system. Blocks COX enzymes to reduce prostaglandins throughout the body [1.4.2].
Gastrointestinal (GI) Side Effects GI side effects like nausea are uncommon and less frequent than with ibuprofen [1.7.3]. More likely to cause stomach problems like indigestion, nausea, and in some cases, ulcers or bleeding [1.5.3].
Cardiovascular Risks Long-term, high-dose use may be associated with a slight increase in blood pressure and heart rate [1.7.3]. Can increase blood pressure and the risk of heart attack or stroke. Should be avoided by people with certain heart conditions [1.5.3].
Blood Thinning Does not have antiplatelet (blood-thinning) effects [1.7.3]. Acts as a blood thinner and should not be taken with other anticoagulants like warfarin [1.5.3].
Asthma Generally considered a safer choice for people with asthma [1.6.2]. Can trigger breathing problems in people with asthma who are sensitive to NSAIDs [1.5.3].
Use in Pregnancy Considered the first-choice painkiller during pregnancy [1.10.1]. Should be avoided by pregnant women [1.5.3].

Populations Requiring Caution

While most people can take paracetamol safely, some individuals should exercise caution and consult a healthcare provider first [1.6.1, 1.6.2]:

  • People with liver or kidney problems.
  • Individuals with chronic alcohol misuse or who drink three or more alcoholic beverages a day. Combining alcohol and paracetamol increases the risk of liver damage [1.11.3].
  • Those who are underweight or malnourished.
  • People taking other medications, especially blood thinners like warfarin, or certain medications for epilepsy or tuberculosis [1.6.1, 1.9.3].

Conclusion

Paracetamol is an effective and safe medication for pain and fever when used according to the label directions. Side effects are rare at therapeutic doses, but they can be severe, with the most critical risk being liver damage from overdose. Understanding the correct dosage, being aware of other medications containing paracetamol, and knowing when to seek medical advice are essential for using this common medicine safely. For more in-depth information, one authoritative source is the NHS page on Paracetamol.

Frequently Asked Questions

While paracetamol is safe for short-term use, long-term daily use has been associated with an increased risk of side effects, including potential liver and kidney damage, and a rise in blood pressure. It's best to use it for the shortest duration necessary and consult a doctor for chronic pain management [1.7.3].

In the first 24 hours, signs can be subtle or non-existent. They may include nausea, vomiting, sweating, loss of appetite, and general malaise. Abdominal pain, especially in the upper-right side, may follow. It's crucial to seek emergency help immediately if an overdose is suspected, even without symptoms [1.3.1, 1.3.2].

Combining regular or heavy alcohol use with paracetamol significantly increases the risk of liver damage (hepatotoxicity). The liver has to process both substances, and doing so simultaneously can overwhelm it, leading to increased production of a toxic metabolite [1.11.1, 1.11.3]. It is best to avoid alcohol when taking paracetamol [1.6.5].

Yes, although it is rare, allergic reactions to paracetamol can occur. Symptoms can range from a mild skin rash and itching to severe reactions like swelling of the face and throat, difficulty breathing (anaphylaxis), and serious skin conditions [1.4.2, 1.4.4].

Observational studies suggest that chronic, high-dose paracetamol use may be linked to an increased risk of adverse cardiovascular events (like stroke), gastrointestinal bleeding, and kidney impairment [1.7.3, 1.7.4]. It is intended for short-term relief.

Yes, paracetamol is widely considered the first-choice painkiller for use during pregnancy. When used at the lowest effective dose for the shortest possible time, it is not known to be harmful to the developing baby [1.10.1, 1.10.2].

Both are safe when used as directed, but their safety profiles differ. Paracetamol has fewer gastrointestinal side effects than ibuprofen but carries a significant risk of liver damage in overdose [1.7.3, 1.5.3]. The 'safer' option depends on an individual's health conditions, such as asthma, heart problems, or pregnancy, where paracetamol is often preferred [1.5.3].

References

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Medical Disclaimer

This content is for informational purposes only and should not replace professional medical advice.