Verified
The first few weeks were frustrating because I still had pain and expected the tablets to work immediately. After my blood tests improved, the attacks became less frequent.
17 Oct 2026
Active ingredient: Allopurinol
Allopurinol
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Allopurinol is a prescription medicine for people with chronic gout, hyperuricaemia, selected uric acid kidney stones, or certain tumour lysis syndrome risks. It lowers uric acid production by inhibiting xanthine oxidase, helping prevent future crystal formation and gout flares.
Description
Allopurinol is a prescription xanthine oxidase inhibitor used to control chronic gout, hyperuricaemia, and some uric acid kidney stones. It lowers uric acid production for long-term prevention rather than providing rapid relief during an acute gout attack.
Composition
Allopurinol is a prescription medicine containing the active substance allopurinol. It is available as oral tablets and works by inhibiting xanthine oxidase to lower uric acid production. The exact tablet strength and other pack details should be checked on the product packaging and prescribed instructions.
Dosage and usage
Allopurinol tablets are taken by mouth. The appropriate strength and schedule depend on the treatment indication, kidney function, age, concurrent medicines, and serum urate response.
- Take the prescribed dose at the same time each day.
- Swallow the tablet with water.
- Taking it after food may reduce stomach discomfort.
- Continue treatment regularly unless the prescriber changes the plan.
- Do not double the next dose after a missed dose.
- If a missed dose is remembered near the next scheduled dose, omit the missed dose and return to the usual schedule.
- Dose increases are normally gradual rather than abrupt.
- People with reduced kidney function may require a lower starting dose or slower adjustment.
The treatment plan may continue for months or years because gout is driven by long-term urate accumulation. Stopping after symptoms improve can allow urate levels to rise again, even when the joints feel normal.
Do not crush or chew a tablet unless the specific formulation allows this. The safest approach is to swallow it with sufficient water and remain consistent with the prescribed schedule.
A common practical mistake is taking Allopurinol only when a joint begins to hurt. Its role is prevention, so intermittent use can leave urate control unstable.
Blood tests may be used to monitor serum urate, kidney function, and liver function. A temporary increase in gout flares can occur after urate-lowering treatment begins because stored crystals are being mobilised. That possibility is managed through an individual flare-prevention plan rather than by stopping Allopurinol without medical direction.
How it works
Purines are natural compounds found in human cells and in some foods. When the body breaks purines down, hypoxanthine is converted to xanthine, and xanthine is then converted to uric acid.
Xanthine oxidase controls these final steps. Allopurinol and its active metabolite oxypurinol inhibit xanthine oxidase, reducing the conversion of hypoxanthine and xanthine into uric acid. The kidneys then handle a lower uric acid burden.
The sequence is:
- Purines are broken down into hypoxanthine.
- Hypoxanthine becomes xanthine.
- Xanthine oxidase normally produces uric acid.
- Allopurinol inhibits this enzyme.
- Serum and urinary uric acid levels can fall.
This mechanism differs from a uricosuric medicine, which increases urinary uric acid excretion. It also differs from enzyme replacement treatment, which breaks down uric acid after it has formed.
A useful clinical detail is that the urate-lowering effect is gradual. The absence of an immediate change in joint pain does not mean that the enzyme inhibition is failing. Treatment response is assessed through symptoms, serum urate, kidney function, and the presence of tophi or recurrent attacks.
Indications
Clinical indications and therapeutic uses of Allopurinol
| Clinical use | Therapeutic goal | Practical meaning |
|---|---|---|
| Chronic gout and hyperuricaemia | Lower serum urate | Reduce future crystal formation and gout flares |
| Uric acid kidney stones | Reduce uric acid load | Help limit recurrence in selected patients |
| Tumour lysis syndrome risk | Limit uric acid production | Support prevention during selected cancer treatments |
Management of chronic gout and hyperuricaemia
Gout develops when monosodium urate crystals form inside or around joints. These crystals trigger inflammation, causing pain, swelling, warmth, and restricted movement. Hyperuricaemia means that urate levels in the blood remain high enough to increase the chance of crystal formation.
Allopurinol lowers the biochemical production of uric acid. With continued treatment, serum urate can fall to a level where existing crystals gradually dissolve and new deposits become less likely. This reduces the frequency of gout attacks over time and may help prevent chronic joint damage.
The medicine does not work like an acute anti-inflammatory treatment. Colchicine, a non-steroidal anti-inflammatory medicine, or another clinician-selected treatment may be used for an acute flare. Starting, stopping, or changing Allopurinol during a flare requires an individual treatment plan because urate shifts can temporarily affect symptoms.
The American College of Rheumatology recommends a treat-to-target approach for gout, with serum urate monitoring used to guide long-term therapy [1].
Prevention of uric acid kidney stones
Uric acid lithiasis occurs when urine contains enough uric acid for crystals or stones to form. Allopurinol can reduce uric acid production in selected patients whose stones are linked to excessive uric acid generation.
Kidney stone prevention also depends on adequate fluid intake and the management of other urinary risk factors. A person with repeated stones may need urine testing, kidney-function assessment, or imaging. Allopurinol is not a treatment for every type of kidney stone.
Tumour lysis syndrome
Rapid destruction of cancer cells can release purines, which are then converted into uric acid. This process is known as tumour lysis syndrome. Allopurinol may be prescribed before or during selected cancer treatments to reduce new uric acid formation.
The risk of tumour lysis syndrome depends on the cancer type, tumour burden, treatment regimen, kidney function, and baseline uric acid level. Hospital teams may select a different urate-lowering approach when uric acid is already markedly elevated or when rapid reduction is required.
Allopurinol is a prevention medicine. It should not be expected to stop the pain of an acute gout attack within hours.
Comparison
Allopurinol is a xanthine oxidase inhibitor. Other urate-lowering options work through different pathways and are selected when response, tolerance, kidney function, cardiovascular risk, or treatment setting makes another approach more appropriate.
| Treatment category | Main action | Clinical position |
|---|---|---|
| Allopurinol | Inhibits xanthine oxidase and reduces uric acid production | Common long-term first-line option for gout |
| Febuxostat | Inhibits xanthine oxidase through a different molecular structure | Considered when Allopurinol is unsuitable or insufficient |
| Uricosuric treatment | Increases renal uric acid excretion | Selected patients with suitable kidney function and urinary risk profile |
Probenecid and sulfinpyrazone are uricosuric medicines. They may be less suitable when kidney function is poor or when uric acid stones are a concern. Febuxostat also inhibits xanthine oxidase, but cardiovascular history and local prescribing guidance influence its use.
Rasburicase is an enzyme treatment used in selected tumour lysis settings. Pegloticase is an intravenous uricase treatment reserved for severe, refractory gout under specialist supervision. It is not a routine substitute for oral Allopurinol.
Combination treatment, such as an xanthine oxidase inhibitor with a uricosuric medicine, may be considered when serum urate remains above target. The choice depends on clinical response rather than on a simple ranking of medicines.
Contraindications
- Previous serious hypersensitivity to Allopurinol
- A previous severe skin reaction caused by Allopurinol
- Significant kidney impairment
- Liver disease
- A history of unexplained blood-count abnormalities
- Current treatment with azathioprine or mercaptopurine
- Pregnancy or breastfeeding, where the expected benefit and alternatives require assessment
- A current widespread rash after starting treatment
- Use of medicines that may increase the risk of severe skin reactions
The most clinically important interaction is with azathioprine and mercaptopurine, also called 6-mercaptopurine. Allopurinol inhibits the breakdown of these purine analogues, which can cause severe bone-marrow suppression unless the combination is deliberately adjusted and monitored.
When this is not for you
Allopurinol is not suitable for everyone. NOT for you if you have had a severe reaction to Allopurinol, cannot complete the required monitoring, or have a clinical situation for which another urate-lowering strategy is safer.
Tell the prescriber about previous reactions to medicines, kidney disease, and any history of severe skin peeling before the first dose. These details can change the treatment choice.
A person with a previous severe reaction should not restart Allopurinol unless a specialist has established a safe and necessary plan. Rechallenge after Stevens–Johnson syndrome or toxic epidermal necrolysis can be dangerous.
Kidney impairment affects oxypurinol clearance. This can increase exposure and may raise the risk of toxicity, so renal function is relevant when selecting the starting dose and reviewing treatment.
Side effects
Many people tolerate Allopurinol without serious problems. Possible unwanted effects include nausea, diarrhoea, stomach discomfort, headache, dizziness, and a skin rash. These effects can occur early in treatment or after a dose change.
A rash requires prompt attention.
Allopurinol can rarely cause severe cutaneous adverse reactions, including Stevens–Johnson syndrome and toxic epidermal necrolysis. These conditions can begin with a rash and progress to blistering, skin peeling, mouth ulcers, eye irritation, fever, facial swelling, or marked illness. Any new rash after starting Allopurinol requires urgent medical assessment, especially when it occurs with fever or mucosal sores.
Stop taking further doses and seek urgent medical care if a new rash is accompanied by:
- Blisters or skin peeling
- Sores in the mouth, eyes, or genital area
- Fever or flu-like symptoms
- Facial swelling
- Difficulty breathing
- Widespread skin tenderness
HLA-B58:01 is a genetic marker associated with a higher risk of severe allopurinol hypersensitivity. The risk varies between populations and is also influenced by kidney disease and other clinical factors. Pharmacogenetic guidance from CPIC supports targeted consideration of HLA-B58:01 testing in groups with increased genetic risk, rather than assuming that universal testing is necessary [2].
The first few weeks deserve close attention. A rash that looks minor can be the earliest sign of a serious reaction, so covering it with an over-the-counter cream and waiting several days is unsafe.
Common mistakes
Several avoidable mistakes can reduce treatment success or increase risk:
- Taking Allopurinol only during painful attacks
- Stopping when the joints feel better
- Doubling a dose after forgetting a tablet
- Ignoring a new rash
- Starting a supplement or anti-inflammatory medicine without checking interactions
- Failing to mention kidney disease
- Taking azathioprine or mercaptopurine without disclosing it
- Expecting immediate pain relief
- Missing urate and kidney-function monitoring
- Changing the schedule repeatedly from day to day
One subtle mistake is confusing a temporary early flare with treatment failure. Urate-lowering therapy can change crystal dynamics during the first phase of treatment. The response should be judged through the planned clinical review, not by one isolated painful day.
Another is treating hydration as a replacement for urate control. Drinking enough fluid supports kidney health, but it does not replace a medicine that blocks uric acid production when Allopurinol is indicated.
Keep the daily dose linked to a routine event, such as the evening meal, if that timing matches the prescribed schedule. A fixed routine is easier to maintain than taking tablets only when symptoms appear.
What doctors say
Doctors generally frame Allopurinol as a long-term risk-reduction treatment. The goal is to lower urate sufficiently to prevent new crystal formation and gradually clear existing deposits, not simply to treat the next painful joint.
A clinician will usually assess:
- Frequency and severity of gout attacks
- Serum urate concentration
- Kidney function
- Liver function when relevant
- Presence of tophi or joint damage
- History of kidney stones
- Other medicines and interaction risks
- Previous rashes or allergic reactions
- Cardiovascular and cancer-treatment circumstances
Treatment is often adjusted using blood-test results rather than symptoms alone. A person can feel well while urate remains high, and a person can experience a flare while long-term treatment is beginning to work.
Doctors also warn against stopping Allopurinol abruptly after a flare settles. The medicine controls the underlying urate burden, so stopping can allow the biochemical problem to return.
Frequently asked questions
Is Allopurinol used for an acute gout attack?
Allopurinol is mainly used for long-term urate reduction and gout prophylaxis, not immediate pain relief. Acute attacks are managed with an anti-inflammatory treatment selected according to kidney function, stomach risk, cardiovascular history, and other medicines. The NHS explains that Allopurinol reduces uric acid over time and is taken regularly for prevention, with guidance reviewed in 2024 [3].
How long does Allopurinol take to work?
The biochemical effect begins after treatment starts, but symptom improvement and reduction in gout attacks can take longer. Existing urate crystals need time to dissolve, and early flares may occur while serum urate is changing. The 2020 American College of Rheumatology guideline supports gradual dose adjustment guided by serum urate rather than relying only on immediate symptom relief .
Can Allopurinol cause a skin rash?
Yes. A mild rash can occur, but any new rash after starting Allopurinol needs prompt medical assessment because severe reactions can begin with apparently limited skin changes. The U.S. FDA prescribing information describes severe cutaneous reactions, including Stevens–Johnson syndrome and toxic epidermal necrolysis, as serious warnings associated with treatment [4].
Can Allopurinol be taken with azathioprine?
The combination can cause severe toxicity because Allopurinol reduces azathioprine breakdown. It should only be used under a deliberately adjusted regimen with appropriate blood-count monitoring. The British National Formulary and regulatory prescribing information published in 2024 treat this as a major interaction rather than a routine combination.
Does Allopurinol protect against kidney stones?
Allopurinol may help prevent uric acid kidney stones when excess uric acid production contributes to stone formation. It does not prevent every type of kidney stone, and stone analysis or urine testing may be needed to identify the cause. The European Medicines Agency describes xanthine oxidase inhibition as the basis for reducing uric acid production in relevant clinical conditions [5].
Does Allopurinol need to be taken for life?
Some people require long-term or lifelong treatment because the tendency to produce excess uric acid persists. Others may have a different duration depending on the cause of hyperuricaemia, cancer-treatment risk, kidney function, stone history, and serum urate response. NHS guidance published in 2024 advises that stopping should follow a planned clinical review because symptoms can improve before the underlying urate burden has been controlled.
Is HLA-B*58:01 testing relevant before Allopurinol?
HLA-B*58:01 testing can help identify people with a higher genetic risk of severe allopurinol hypersensitivity. The value of testing depends on ancestry, local prevalence, kidney function, and clinical guidance. CPIC pharmacogenetic recommendations published in 2015 support avoiding Allopurinol in individuals who test positive when an appropriate alternative is available .
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Allopurinol: Reviews and Experiences
3.9
Based on 4 reviews
Verified
I developed a scattered rash after starting treatment and stopped taking further doses while seeking urgent medical advice. The rash was taken seriously, which made me more cautious about restarting any similar medicine.
30 Sept 2026
Verified
The main benefit was fewer attacks and less swelling in my toe joints. I still needed regular testing, and missing tablets for several days seemed to make control less reliable.
26 Oct 2026
Verified
My stomach felt unsettled at first, especially when I took the tablet without food. Taking it after a meal made the routine easier, although the schedule still needed monitoring.
11 Oct 2026
Sources
- American College of Rheumatology (2020). 2020 American College of Rheumatology Guideline for the Management of Gout.
- Clinical Pharmacogenetics Implementation Consortium (2015). CPIC Guidelines for HLA-B Genotype and Allopurinol Dosing.
- NHS (2024). How and when to take allopurinol.
- U.S. Food and Drug Administration (2024). Allopurinol prescribing information.
- EMA (2018). Summary of Product Characteristics (SmPC) — allopurinol.
