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Limited evidencePhysical performance

Inosine

Inosine was a 1980s-90s sports supplement that failed every controlled performance test, then had a second life as a urate-raising neuroprotectant for Parkinson's disease — until a phase 3 trial was stopped for futility. There is no good reason to take it, and a concrete reason not to.

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What the science says

  • Does not improve exercise performance — repeatedly Limited evidence

    Ten competitive male cyclists took 5,000 mg/day for 5 days in a placebo-controlled study: no differences in Wingate peak power, end power, fatigue index, total work or post-test lactate, and no difference in work completed during a 30-minute self-paced ride. Time to fatigue in a supramaximal sprint was actually shorter on inosine (99.7 s) than placebo (109.7 s, p < 0.05). Earlier work on 3-mile treadmill run performance and VO2 peak, and a later cycling trial, reported the same absence of benefit. Serum uric acid rose, confirming subjects absorbed the dose — it simply did nothing useful.

  • Failed a phase 3 Parkinson's disease trial Strong evidence

    SURE-PD3 randomized 298 people with early Parkinson's disease and low baseline urate to inosine or placebo for up to 2 years. Inosine raised serum urate by 2.03 mg/dL from a 4.6 mg/dL baseline — a 44% increase, so the target was engaged — yet MDS-UPDRS progression was 11.1 points/year on inosine versus 9.9 on placebo (difference 1.26, 95% CI -0.59 to 3.11, p = 0.18). The study closed early on a prespecified futility analysis. This is a well-powered negative result and it settles the question.

  • Raising uric acid is the side effect, not the benefit Moderate evidence

    Inosine is a purine nucleoside that metabolizes to uric acid — that is its entire pharmacology. In SURE-PD3, the inosine arm had a markedly higher rate of kidney stones, the predictable consequence of sustained hyperuricemia. Any supplement whose measurable effect on your body is raising urate should be judged against the well-established harms of high urate: gout and urolithiasis.

Dosage & safety

Studied dosePerformance studies used 5,000-6,000 mg/day for 2-5 days. SURE-PD3 titrated 500-3,000 mg/day (up to 2 g three times daily) to a serum urate target of 7.1-8.0 mg/dL, under medical supervision with urate monitoring and stone surveillance. Neither regimen is appropriate for self-directed use — the first because it does not work, the second because it requires monitoring and still did not work.
SafetyThe principal hazard is uric acid elevation: kidney stones (significantly increased in the phase 3 trial) and precipitation of gout flares. Contraindicated in anyone with gout, existing hyperuricemia, a history of urate kidney stones, or renal impairment. GI upset is common. It directly opposes urate-lowering therapy such as allopurinol or febuxostat. Anyone with a condition predisposing to high purine turnover should avoid it. Sold as a dietary supplement in the US and used medically only within trials. Not on the WADA prohibited list — a distinction of no practical value for a supplement with a consistent record of not enhancing performance.

How to take it

TimingThere is no useful schedule because there is no useful dose — the performance trials found no benefit and the Parkinson's trial found harm.
With food?With food to limit GI upset, if you take it despite the above.
Worth knowingAnyone who uses it should know their baseline uric acid and stop at the first joint pain or flank pain — kidney stones were significantly increased in the phase 3 trial.

Interactions

With medications

  • allopurinol and febuxostat

    Inosine raises uric acid, directly opposing urate-lowering therapy. do not combine

  • thiazide and loop diuretics

    Both raise uric acid, so the combination compounds gout and stone risk. avoid

Well-established interactions only — this is not a complete list. Always tell your doctor and pharmacist what you take.

Frequently asked questions

Does inosine improve athletic performance?

No. Controlled trials repeatedly found no benefit: competitive cyclists taking 5,000 mg/day of inosine for 5 days showed no gain in power or work, and time to fatigue in a sprint was actually shorter than on placebo. The evidence against inosine as a performance aid is consistent.

Does inosine help Parkinson's disease?

No. The phase 3 SURE-PD3 trial of 298 people with early Parkinson's disease found inosine raised urate as intended but did not slow progression, and the trial was stopped early for futility. It also increased kidney stones.

What are the side effects of inosine?

Inosine is metabolized to uric acid, so its main hazards are kidney stones, which were significantly increased in the phase 3 trial, and gout flares. Avoid inosine if you have gout, high uric acid, urate kidney stones or kidney impairment.

Is inosine safe with allopurinol or diuretics?

No. Inosine raises uric acid and directly opposes allopurinol and febuxostat, and thiazide and loop diuretics also raise uric acid, compounding gout and stone risk. Do not combine inosine with these drugs.

Scientific references

Where to buy

Swanson Vitamins, Inosine, 60 Veggie Caps (500 mg Per cap)

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