Background: Hot flashes are common in menopausal women and significantly affect the quality of life of many patients diagnosed with breast cancer for which hormone replacement therapy is not indicated. In a previous uncontrolled study, guarana (Paullinia cupana) showed significant decreases in the amount and intensity of hot flashes in this group of women. Hypothesis/Purpose: The main objective was to reduce the intensity and frequency of hot flashes with the use of PC-18, compared with placebo in women who survived breast cancer without current evidence of disease. Study Design: The present study consists of a double-blind, randomized, placebo-controlled, uni-institutional, two-arm phase II clinical trial. Methods: The experimental group received the purified dry extract of Paullinia cupana (PC-18) at a dose of 37.5 g twice daily, while the other group received placebo, also twice daily. Results: The study included 40 patients who had completed surgical, chemotherapeutic and/or radiotherapeutic treatment for more than 3 months and who were on adjuvant hormone therapy at the time of inclusion, 20 in each arm. Both groups showed significant reductions in the number and intensity of hot flashes, with no significant difference between the arms. There was a higher intensity and frequency of hot flashes in patients receiving tamoxifen compared with those who received aromatase inhibitors. The toxicities observed were not very significant. Conclusion: This concludes that PC-18 did not demonstrate significantly greater capacity than placebo for control of hot flashes in women with a history of breast cancer and adjuvant hormone therapy.