Purpose Therapies for breast cancer may induce hot flashes that can affect quality of life. We undertook a double-blind, placebo-controlled trial with the primary objective of comparing the average daily hot flash scores in the twelfth week among patients treated with venlafaxine, clonidine, and placebo. Additional analyses of the hot flash score over the full 12 weeks of treatment were performed. Patients and Methods In all, 102 patients with a history of breast cancer were randomly assigned (2:2:1) to venlafaxine 75 mg, clonidine 0.1 mg, or placebo daily for 12 weeks. Questionnaires at baseline and during treatment assessed daily hot flash scores, sexual function, sleep quality, anxiety, and depression. Results After 12 weeks, a total of 80 patients were evaluable for the primary end point. During week 12, hot flash scores were significantly lower in the clonidine group versus placebo (P = .03); for venlafaxine versus placebo, the difference was borderline not significant (P = .07). However, hot flash scores were equal in the clonidine and venlafaxine groups. Over the course of 12 weeks, the differences between both treatments and placebo were significant (P <.001 for venlafaxine v placebo; P = .045 for clonidine v placebo). Frequencies of treatment-related adverse effects of nausea (P = .02), constipation (P = .04), and severe appetite loss were higher in the venlafaxine group. Conclusion Venlafaxine and clonidine are effective treatments in the management of hot flashes in patients with breast cancer. Venlafaxine resulted in a more immediate reduction of hot flash scores when compared with clonidine; however, hot flash scores at week 12 were lower in the clonidine group than in the venlafaxine group.