Allopurinol is the most commonly prescribed medication for long-term gout management. It works by lowering uric acid levels in your blood, which prevents the painful crystal buildup in joints that causes gout flares. It won’t relieve the pain of an active attack on its own, but taken daily over time, it reduces how often flares happen and can eventually stop them altogether.
How Allopurinol Works
Gout develops when your body has too much uric acid circulating in the blood. That excess uric acid forms sharp, needle-like crystals that deposit in joints, triggering intense inflammation and pain. Allopurinol blocks the enzyme responsible for producing uric acid in the first place, so less of it ends up in your bloodstream. Over months, this also allows existing crystal deposits to gradually dissolve.
The goal is to get your uric acid level below 6 mg/dL and keep it there. The American College of Rheumatology strongly recommends this treat-to-target approach over simply taking a fixed dose and hoping for the best. Your doctor will check your uric acid periodically and adjust your dose until you hit that threshold.
Starting Dose and How It’s Increased
Most people start at 100 mg per day, a deliberately low dose. Every two to five weeks, the dose goes up by 100 mg until your uric acid drops below the target. The maximum is 800 mg daily, though many people reach their target well before that. This slow ramp-up matters because jumping to a high dose too quickly can trigger flares and increases the risk of side effects.
If you have significant kidney problems, the starting dose is typically cut in half to 50 mg daily, with smaller increases of 50 mg at a time. Because allopurinol and its byproducts are cleared through the kidneys, impaired kidney function causes the drug to build up faster. For people with very low kidney function, the maximum dose may be capped at 100 to 200 mg daily depending on how well the kidneys are filtering.
Expect Early Flares
One of the most frustrating parts of starting allopurinol is that it can temporarily make gout worse. As uric acid levels drop, existing crystal deposits shift and partially dissolve, which can trigger new flares in the first several months of treatment. This doesn’t mean the medication isn’t working. It’s actually a sign that crystal stores are being disrupted.
To blunt these early flares, doctors typically prescribe a low-dose anti-inflammatory medication to take alongside allopurinol for the first several months. In a clinical trial comparing colchicine prophylaxis to placebo during the start of allopurinol therapy, patients on colchicine averaged only 0.52 flares over six months compared to 2.91 flares without it. The flares that did occur were also less severe. Six months of prophylaxis is the duration best supported by evidence, though your doctor may adjust based on your history.
Can You Start It During a Flare?
For years, the standard advice was to wait until an active gout attack fully resolved before starting allopurinol. That thinking has shifted. A randomized clinical trial found that initiating low-dose allopurinol during an acute, treated flare did not significantly prolong the attack. Patients who started allopurinol during a flare resolved in about 15 days on average, compared to 13 days for those on placebo, a difference that was not statistically meaningful. Current guidelines from the American College of Rheumatology reflect this, noting that starting during a flare is acceptable as long as the flare itself is being treated with appropriate anti-inflammatory medication.
Side Effects
Most people tolerate allopurinol well, especially when the dose is increased gradually. The most common side effects are mild: skin rash, nausea, diarrhea, and occasionally abnormal liver function tests. A rash in the first few weeks is relatively common and should prompt a conversation with your doctor, because in rare cases it can signal the beginning of a more serious reaction.
The serious concern is a condition called severe cutaneous adverse reaction, which can cause widespread skin blistering, organ damage, and in some cases can be fatal. This reaction is strongly linked to a genetic marker called HLA-B*58:01. The allele is most common in people of Southeast Asian descent: roughly 10 to 15% of Han Chinese individuals carry it, about 12% of Koreans, and 6 to 8% of people of Thai descent. It’s also more common in African Americans. Among Europeans and Japanese populations, the frequency is only about 1 to 2%. The American College of Rheumatology recommends genetic testing before starting allopurinol if you are of Southeast Asian or African American descent. If you carry the allele, allopurinol should not be used, and an alternative medication can be prescribed instead.
A Critical Drug Interaction
If you take azathioprine or its related compound 6-mercaptopurine, commonly used for autoimmune conditions, organ transplants, or certain cancers, combining them with allopurinol is dangerous without careful dose adjustments. Allopurinol blocks the same enzyme that breaks down these drugs, causing their active compounds to build up to toxic levels. The result can be severe suppression of bone marrow function, leading to dangerously low blood cell counts.
When the combination truly cannot be avoided, the dose of azathioprine or 6-mercaptopurine needs to be cut to about 25% of the standard dose. Blood counts must be monitored weekly for the first three months and monthly after that. If you’re prescribed allopurinol and already take either of these medications, make sure every prescribing doctor is aware of both.
What Long-Term Treatment Looks Like
Allopurinol is a daily, lifelong medication for most people with gout. It doesn’t cure the underlying tendency to overproduce or under-excrete uric acid. If you stop taking it, uric acid levels rise again and flares return, often within months. The payoff for sticking with it is substantial: once uric acid stays below 6 mg/dL long enough for existing crystal deposits to dissolve (which can take one to two years depending on how much crystal burden you started with), many people become completely flare-free.
The medication is inexpensive, available as a generic, and taken once daily, which makes adherence straightforward for most people. Periodic blood work to check uric acid and kidney and liver function is the main ongoing requirement. For the majority of gout patients, allopurinol remains the first-line choice for long-term management precisely because it’s effective, well-studied, and well-tolerated when started and dosed correctly.