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Alka-Seltzer XS - 20 Tablets

Alka-Seltzer XS - 20 Tablets

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  • ✔️ Relieves headache, cold symptoms, and mild pain simultaneously
  • ✔️ Triple-action formula: aspirin, paracetamol, and caffeine combined
  • ✔️ Effervescent format for faster absorption than standard tablets
  • ✔️ Caffeine adjuvant clinically shown to enhance analgesic effectiveness
  • ✔️ Suitable for adults and young people aged 16 and over

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What Are Alka-Seltzer XS Tablets and How Do They Help?

 

If you've ever woken up with a pounding head, a blocked nose, and that general feeling of being run down, you'll know how much you just want something that works quickly. Alka-Seltzer XS tablets are an effervescent, over-the-counter analgesic that combines three active ingredients — aspirin, paracetamol, and caffeine — to tackle headache, cold symptoms, and mild to moderate pain all at once. Each pack contains 20 tablets, making it a practical option to keep in your medicine cabinet at home or at work. At just £5.79, it's an accessible choice for everyday symptom relief without needing a prescription.

Alka-Seltzer XS is classified as a General Sale List (GSL) medicine in the UK, meaning it can be purchased without a pharmacist's supervision. That said, it still contains active ingredients that carry real clinical considerations — so reading the label carefully matters. If you're looking for broader pain relief options, Cured Pharmacy stocks a wide range of products to suit different needs and preferences.

 

How Does Alka-Seltzer XS Work in the Body?

 

The three-ingredient combination in Alka-Seltzer XS is what sets it apart from single-ingredient analgesics. Each ingredient plays a distinct role:

  • Aspirin (267mg per tablet): A non-steroidal anti-inflammatory drug (NSAID) that inhibits prostaglandin synthesis, reducing pain, inflammation, and fever.
  • Paracetamol (133mg per tablet): Works centrally to raise the pain threshold and reduce fever, complementing aspirin's peripheral action.
  • Caffeine (40mg per tablet): Acts as an adjuvant analgesic — clinical evidence shows caffeine can enhance the pain-relieving effect of both aspirin and paracetamol by up to 40% when used in combination.
  • Effervescent delivery: Dissolving the tablets in water means the active ingredients are absorbed more rapidly compared to standard solid tablets, which may mean faster onset of action.

The effervescent formulation also produces a slightly alkaline solution, which may be gentler on the stomach lining than taking aspirin in solid tablet form — though it is still not recommended for people with a history of peptic ulcers.

 

Who Is Alka-Seltzer XS Suitable For?

 

Alka-Seltzer XS is designed for adults and young people aged 16 and over. It's particularly useful when you're dealing with more than one symptom at the same time — for instance, a headache alongside cold-related aches and a mild fever. It is not a substitute for targeted cold and flu treatments, but it can provide meaningful short-term relief.

This product may suit you if you:

  • Are aged 16 or over and in generally good health
  • Experience tension headaches, mild migraines, or cold-related head pain
  • Need relief from mild to moderate musculoskeletal pain (e.g. back ache, period pain)
  • Prefer an effervescent format that dissolves quickly and is easy to swallow

It is not suitable for children under 16 due to the aspirin content and the associated risk of Reye's syndrome, a rare but serious condition. Pregnant women, particularly in the third trimester, should avoid aspirin-containing products unless specifically directed by a doctor.

 

How Does Alka-Seltzer XS Compare to Standard Paracetamol Tablets?

 

Feature Alka-Seltzer XS Standard Paracetamol 500mg
Active ingredients Aspirin, Paracetamol, Caffeine Paracetamol only
Formulation Effervescent tablet (dissolved in water) Solid tablet (swallowed whole)
Suitable for under 16s No Yes (age-appropriate doses)
Anti-inflammatory action Yes (aspirin) No
Caffeine adjuvant Yes No

 

How Should You Store Alka-Seltzer XS Tablets?

 

Store your Alka-Seltzer XS tablets below 25°C in a dry place, away from direct sunlight and moisture. The effervescent tablets are particularly sensitive to humidity — even brief exposure to damp air can cause them to begin dissolving prematurely in the foil. Always reseal the packaging after use and keep the product out of reach and sight of children.

Check the expiry date printed on the packaging before use. Do not use the tablets if the foil is damaged or if the tablets appear discoloured or crumbly. If you're building up a home medicine kit alongside products like cold and flu remedies, storing everything in a cool, dry cupboard (not a bathroom cabinet) is generally the best approach.

This product is a medicine. Speak to your doctor or pharmacist before using if you have an underlying medical condition or are taking other medicines.

Alka-Seltzer XS 20 Tablets specifications
Treatment category Analgesic / Cold and flu symptom relief
Mechanism of action Prostaglandin synthesis inhibition (aspirin), central pain threshold elevation (paracetamol), adjuvant analgesia (caffeine)
Effective for Headache, mild to moderate pain, cold symptoms, fever
Suitable for Adults and young people aged 16 and over
Active ingredients Aspirin 267mg, Paracetamol 133mg, Caffeine 40mg (per tablet)
Pack size 20 tablets
UK classification General Sale List (GSL)
Drug class NSAID / Analgesic combination
Preparation Effervescent tablet
Route of administration Oral (dissolved in water)

Specifications of Alka-Seltzer XS 20 Tablets

 

What Is Alka-Seltzer XS and What Is It Used For?

 

Alka-Seltzer XS is an effervescent analgesic tablet used for the short-term relief of headache, cold and flu symptoms, mild to moderate pain, and fever. It contains a combination of aspirin (267mg), paracetamol (133mg), and caffeine (40mg) per tablet. The effervescent format means the tablets dissolve in water before you drink them, which may support faster absorption compared to conventional solid tablets. It is an over-the-counter product available without a prescription for adults and young people aged 16 and over.

 

What Do You Need to Know Before Using Alka-Seltzer XS?

 

Before taking Alka-Seltzer XS, it's important to check whether it is appropriate for you. Do not take this medicine if any of the following apply:

  • You are under 16 years of age (risk of Reye's syndrome with aspirin)
  • You are allergic to aspirin, paracetamol, caffeine, or any other NSAIDs
  • You have or have had a peptic ulcer or stomach bleeding
  • You are in the third trimester of pregnancy
  • You have severe kidney, liver, or heart failure
  • You have haemophilia or another bleeding disorder
  • You are taking methotrexate at a dose of 15mg or more per week

The following medicines may interact with Alka-Seltzer XS. Always tell your pharmacist or doctor what you are taking:

  • Anticoagulants (e.g. warfarin, heparin) — aspirin increases bleeding risk
  • Other NSAIDs (e.g. ibuprofen) — increased risk of gastrointestinal side effects
  • Other paracetamol-containing products — risk of paracetamol overdose
  • Antidepressants (SSRIs) — may increase bleeding risk when combined with aspirin
  • Antidiabetic medicines — aspirin may enhance the glucose-lowering effect
  • Corticosteroids — increased risk of gastrointestinal bleeding

 

How Should You Use Alka-Seltzer XS?

 

Always use Alka-Seltzer XS exactly as described on the label or as directed by your pharmacist. Do not exceed the stated dose. The effervescent tablets must be dissolved in water before taking — never swallow them whole or chew them.

  1. Fill a glass with at least 200ml of water (roughly a standard drinking glass).
  2. Drop 2 tablets into the water.
  3. Wait until the tablets have fully dissolved — this usually takes around 1–2 minutes.
  4. Stir gently if needed, then drink the solution immediately.
  5. Repeat after 4 hours if symptoms persist, but do not take more than 4 doses (8 tablets) in any 24-hour period.
Indication Age Group Dose Frequency
Headache / mild pain Adults & young people 16+ 2 tablets dissolved in water Every 4 hours, max 4 doses/24hrs
Cold and flu symptoms Adults & young people 16+ 2 tablets dissolved in water Every 4 hours, max 4 doses/24hrs
Under 16 years Children Not suitable Not applicable

 

What Are the Possible Side Effects of Alka-Seltzer XS?

 

Like all medicines, Alka-Seltzer XS can cause side effects, although not everyone experiences them. If you're concerned about any reaction, stop taking the tablets and speak to your pharmacist or GP. You can also browse our indigestion treatments if stomach discomfort becomes an issue.

Common side effects (may affect up to 1 in 10 people):

  • Nausea or stomach discomfort
  • Heartburn or indigestion
  • Mild stomach pain

Less common side effects (may affect up to 1 in 100 people):

  • Gastrointestinal bleeding (seek immediate medical attention if you notice blood in stools or vomit)
  • Allergic reactions including skin rash, itching, or swelling
  • Bronchospasm (wheezing or difficulty breathing) — particularly in people with aspirin-sensitive asthma
  • Tinnitus (ringing in the ears) at higher doses
  • Dizziness or headache (paradoxically, with overuse)

 

How Should You Store Alka-Seltzer XS?

 

Correct storage helps maintain the quality and effectiveness of your tablets. Follow these guidelines:

  • Store below 25°C in a cool, dry place
  • Keep away from direct sunlight and sources of moisture
  • Do not store in a bathroom cabinet — humidity can degrade effervescent tablets
  • Keep out of reach and sight of children
  • Do not use after the expiry date printed on the packaging
  • Do not use if the foil blister is damaged or the tablets appear discoloured

If you need to dispose of unused tablets, do not flush them down the toilet or pour them down the drain. Return them to your local pharmacy for safe disposal. For general health maintenance alongside pain relief, you might also find our vitamins and supplements range useful to support your overall wellbeing.

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Your safety and success are our highest priorities. Our medical team rigorously evaluates every product and piece of advice we provide, ensuring you receive only the most effective, science-backed solutions available.

Frequently Asked Questions

Where can I buy Alka-Seltzer XS tablets online in the UK?

You can buy Alka-Seltzer XS 20 Tablets directly from Cured Pharmacy, a GPhC-registered UK online pharmacy, for just £5.79. No prescription is needed as it is an over-the-counter medicine. Simply add it to your basket and it will be dispatched promptly to your door.

How does Alka-Seltzer XS work in the body?

Alka-Seltzer XS contains three active ingredients that work together: aspirin inhibits prostaglandin production to reduce pain and inflammation, paracetamol raises the central pain threshold and lowers fever, and caffeine acts as an adjuvant that enhances the effectiveness of both analgesics. The effervescent format allows the ingredients to be absorbed quickly once dissolved in water. This combination approach means it can address multiple symptoms simultaneously.

How do I use Alka-Seltzer XS step by step?

Drop 2 tablets into a glass containing at least 200ml of water and wait for them to fully dissolve before drinking — this usually takes around 1 to 2 minutes. Never swallow the tablets whole or chew them. Drink the solution as soon as it is fully dissolved for best results.

What is the correct dose of Alka-Seltzer XS for adults?

The recommended dose for adults and young people aged 16 and over is 2 tablets dissolved in water. You can repeat this dose every 4 hours if needed, but you must not exceed 8 tablets (4 doses) in any 24-hour period. Always follow the instructions on the packaging and do not take more than the stated dose.

What is the best time to take Alka-Seltzer XS?

Take Alka-Seltzer XS as soon as your symptoms begin — early use tends to be more effective for headache and cold-related discomfort. Taking it with or after food may help reduce the chance of stomach irritation, particularly given the aspirin content. Avoid taking it late at night if you are sensitive to caffeine, as the 80mg of caffeine per dose (from 2 tablets) may affect sleep.

What are the side effects of Alka-Seltzer XS?

Common side effects include nausea, stomach discomfort, and heartburn. Less commonly, some people may experience gastrointestinal bleeding, allergic skin reactions, or bronchospasm — particularly those with aspirin-sensitive asthma. If you notice any unusual or severe symptoms, stop taking the tablets and seek medical advice promptly. You can find further pain relief alternatives if Alka-Seltzer XS is not suitable for you.

Who should not take Alka-Seltzer XS?

Alka-Seltzer XS is not suitable for children under 16 years of age due to the risk of Reye's syndrome associated with aspirin. It should also be avoided by people with a known allergy to aspirin or NSAIDs, those with active peptic ulcers, anyone in the third trimester of pregnancy, and people with severe liver, kidney, or heart failure. Always read the full list of contraindications on the packaging before use.

Can I take Alka-Seltzer XS with other medicines?

You should not take Alka-Seltzer XS alongside other aspirin or paracetamol-containing products, as this increases the risk of overdose. It can also interact with anticoagulants such as warfarin, other NSAIDs, SSRIs, corticosteroids, and antidiabetic medicines. Always check with your pharmacist before combining it with any other medication.

What happens if I miss a dose of Alka-Seltzer XS?

Alka-Seltzer XS is taken as needed for symptom relief rather than on a fixed schedule, so there is no "missed dose" in the traditional sense. Simply take your next dose when symptoms return, provided at least 4 hours have passed since your last dose. Never double up to compensate for a missed dose.

How long can I use Alka-Seltzer XS for?

Alka-Seltzer XS is intended for short-term use only. The NHS advises not using aspirin-containing products for fever for more than 3 days, or for pain for more than 5 days, without consulting a doctor or pharmacist. If your symptoms persist or worsen beyond these timeframes, seek professional medical advice rather than continuing self-treatment.

Is Alka-Seltzer XS suitable during pregnancy or breastfeeding?

Alka-Seltzer XS is not recommended during pregnancy, particularly in the third trimester, as aspirin can affect the foetal circulation and may cause complications during labour. If you are breastfeeding, aspirin is generally not recommended as it passes into breast milk. Speak to your GP or midwife before taking any pain relief during pregnancy or while breastfeeding.

What are the alternatives to Alka-Seltzer XS?

If Alka-Seltzer XS is not suitable for you, alternatives include standard paracetamol tablets, ibuprofen, or other combination cold and flu remedies. You can explore a full range of options in our cold and flu collection. Your pharmacist can help you choose the most appropriate product based on your symptoms and medical history.

Does Alka-Seltzer XS contain caffeine?

Yes — each tablet contains 40mg of caffeine, so a standard 2-tablet dose provides 80mg of caffeine in total. This is roughly equivalent to one standard cup of coffee. If you are sensitive to caffeine or are trying to limit your intake, factor this into your daily consumption, particularly if you are taking multiple doses throughout the day.

Can I drink alcohol while taking Alka-Seltzer XS?

You should avoid alcohol while taking Alka-Seltzer XS. Combining alcohol with aspirin significantly increases the risk of gastrointestinal bleeding and stomach irritation. Alcohol also interacts with paracetamol and can increase the risk of liver damage, particularly if you drink regularly or in large amounts. The NHS advises caution with alcohol and aspirin-containing medicines.

What are the latest findings on caffeine as an analgesic adjuvant?

Research published in clinical literature supports the use of caffeine as an adjuvant analgesic, with studies suggesting it can enhance the pain-relieving effect of aspirin and paracetamol by a meaningful margin when used in combination. The Cochrane Collaboration has reviewed evidence showing that adding caffeine to standard analgesics provides a modest but clinically relevant improvement in pain relief for headache and other acute pain conditions. This is the rationale behind the formulation of products like Alka-Seltzer XS.

How Should You Use Alka-Seltzer XS?

Alka-Seltzer XS must always be dissolved in water before you take it — never swallow the tablets whole or chew them. The effervescent action is part of how the medicine works, and skipping this step means the tablets won't dissolve properly and could cause irritation. Follow these steps each time you take a dose:

What Is the Correct Dose of Alka-Seltzer XS?

Always follow the dosage instructions on the packaging. Taking more than the recommended dose does not improve symptom relief and increases the risk of side effects, particularly from the aspirin and paracetamol components. The table below summarises the correct dosing by indication and age group.

When Is the Best Time to Use Alka-Seltzer XS?

Take Alka-Seltzer XS as soon as your symptoms begin — acting early tends to give better results, particularly for headache. Because the tablets contain aspirin, taking them with or shortly after food can help reduce the likelihood of stomach irritation. Bear in mind that each 2-tablet dose contains 80mg of caffeine, so if you are sensitive to caffeine or it is late in the day, consider whether this could affect your sleep before taking a dose.

How Long Can You Use Alka-Seltzer XS For?

Alka-Seltzer XS is designed for short-term symptom relief only. The NHS advises that aspirin-containing products should not be used for fever for more than 3 consecutive days, or for pain for more than 5 consecutive days, without seeking medical advice. If your symptoms do not improve within these timeframes, or if they worsen at any point, stop taking the tablets and consult your GP or pharmacist. Prolonged use without medical supervision is not recommended.

Do not exceed the recommended dose. If in doubt, speak to your pharmacist.

What Are the Most Common Side Effects of Alka-Seltzer XS?

Most people tolerate Alka-Seltzer XS well when taken as directed, but like all medicines containing aspirin and paracetamol, it can cause side effects in some individuals. The most frequently reported issues relate to the gastrointestinal tract, largely due to the aspirin component. Common side effects include:

  • Nausea or feeling sick
  • Stomach discomfort or mild abdominal pain
  • Heartburn or indigestion
  • Dyspepsia (general upper digestive discomfort)

Taking the dissolved solution with or after food may help reduce these effects. If stomach discomfort is persistent, speak to your pharmacist about whether an alternative analgesic might be more suitable for you.

What Are the Less Common Side Effects of Alka-Seltzer XS?

Less commonly, some people may experience more significant reactions. These are not typical but are worth being aware of before you start taking the medicine. Less common side effects include:

  • Gastrointestinal bleeding — signs include blood in stools (dark or tarry stools) or vomiting blood
  • Skin rash, itching, or hives
  • Swelling of the face, lips, or throat (angioedema)
  • Tinnitus (ringing in the ears), particularly at higher doses
  • Dizziness or light-headedness
  • Paradoxical headache with overuse (medication overuse headache)

What Are the Serious Side Effects of Alka-Seltzer XS?

Serious side effects are rare but require immediate medical attention if they occur. Bronchospasm — a sudden tightening of the airways causing wheezing or difficulty breathing — can occur in people with aspirin-sensitive asthma. This is a known contraindication, and anyone with a history of aspirin-induced bronchospasm should not take this product. Severe allergic reactions (anaphylaxis), though very rare, can also occur and require emergency treatment. Signs include sudden swelling, difficulty breathing, and a rapid drop in blood pressure.

What Should You Do If You Experience Side Effects?

If you experience mild side effects such as nausea or heartburn, try taking your next dose with food and ensure you have dissolved the tablets fully in water. For any side effect that is severe, unexpected, or does not resolve, stop taking Alka-Seltzer XS immediately and contact your GP or pharmacist. In the case of a suspected allergic reaction or difficulty breathing, call 999 or go to your nearest A&E department without delay. Do not take a further dose while waiting for medical advice.

Can Alka-Seltzer XS Interact With Other Medicines?

Yes — Alka-Seltzer XS has several clinically significant drug interactions that you need to be aware of. Aspirin increases the anticoagulant effect of warfarin and other blood-thinning medicines, raising the risk of bleeding. Taking it alongside other NSAIDs such as ibuprofen increases the risk of gastrointestinal side effects. Combining it with SSRIs (antidepressants) also raises bleeding risk. Crucially, you must not take Alka-Seltzer XS at the same time as any other paracetamol-containing product — doing so can lead to paracetamol overdose, which can cause serious liver damage even without obvious symptoms. Always tell your pharmacist about every medicine you are taking, including herbal remedies and supplements.

If you are concerned about any side effects, contact your pharmacist or GP immediately.

Patient Information Leaflet

Important - Before taking any medication, it is always important to read the Patient Information Leaflet (PIL)

Written and reviewed by our qualified team

GPhC Number: 2233073
Tarun Kumar

Reviewed by:

Tarun Kumar

Superintendent/ Clinical Lead

📖 Find out more about our team of medical content authors and how we ensure the accuracy of our content with our content guidelines.

Content last updated: 31 Mar 2025

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