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Evidence Explorer / MS-N217 / Botanicals, adulteration and safety / Appraised November 2, 2026

PC-SPES was an eight-herb product marketed for prostate cancer. Trials reported PSA declines, but tested lots contained prescription drugs—including estrogenic compounds—and the product was recalled. The findings cannot be attributed to the herbs or treated as evidence for current substitute products.

Evidence at a glance

  • Population: a randomized phase II crossover trial enrolled 90 men with androgen-independent prostate cancer; 85 were assessable.
  • Comparator: PC-SPES versus diethylstilbestrol (DES), with crossover at progression and prophylactic warfarin.
  • Results: PSA declines of at least 50% occurred in 40% versus 24%; median time to progression was 5.5 versus 2.9 months.
  • Critical limitation: all tested PC-SPES lots contained DES; one also contained ethinyl estradiol. The trial stopped after market withdrawal.
  • Evidence label: uninterpretable efficacy because of adulteration; product withdrawn; thromboembolic and hormonal risk.

What was studied

The multicenter trial randomized participants to three PC-SPES capsules three times daily or DES 3 mg daily. Five thromboembolic events occurred—one with PC-SPES and four with DES. Common effects included fatigue, breast enlargement and breast tenderness.

Chemical analyses found measurable DES in four PC-SPES lots and ethinyl estradiol in one. NCI’s broader review documents other batches containing warfarin and indomethacin and substantial lot-to-lot variation.

What this evidence cannot establish

PSA lowering is not by itself proof of longer survival, and it cannot be assigned to the herbal mixture when active prescription drugs contaminated the tested lots. The trial’s early closure and adulteration make its comparative efficacy findings inconclusive.

The original manufacturer closed and PC-SPES is no longer legally available. Products marketed as substitutes are not the tested formulation and cannot inherit its results.

Practical safety context

Estrogenic exposure can cause breast symptoms, sexual side effects and blood clots. Undeclared warfarin raises bleeding risk; undeclared indomethacin adds gastrointestinal, kidney and cardiovascular risks.

Any supplement marketed as a replacement should be reviewed for independent identity and contaminant testing. PSA changes should be interpreted alongside imaging, symptoms and the full treatment context.

Questions for the care team

  • Is this the withdrawn original product or an untested substitute?
  • Has the batch been independently tested for hormones, anticoagulants, anti-inflammatory drugs and heavy metals?
  • How will clotting, bleeding and cancer progression be monitored?

Sources

Source note: The NCI PDQ and PubMed trial record were checked. The original trial itself concluded that synthetic estrogen adulteration made interpretation problematic. No current legal original PC-SPES formulation or validating uncontaminated randomized trial was identified on November 2, 2026.

This record is educational. PSA changes do not automatically mean improved survival, and adulterated or substitute products should not be used as prostate-cancer treatment.