Many medications have been developed for one purpose but then are found to have other clinical activities. There is tremendous interest in whether non-cancer medications may potentially have effects on breast cancer survival. In this review article, we have presented and evaluated the evidence for several commonly used over-the-counter and prescription medications - including aspirin (and other non-steroidal anti-inflammatory drugs), beta-blockers, angiotensin-converting enzyme inhibitors, statins, digoxin, and metformin - that have been evaluated among breast cancer survivors in prospective studies. Substantial scientific evidence supports the hypothesis that some of these common and relatively safe drugs may reduce breast cancer mortality among those with the disease by an amount that rivals the mortality reduction gained by currently used therapies. In particular, the evidence is strongest for aspirin (approximately 50% reduction), statins (approximately 25% reduction), and metformin (approximately 50% reduction). As these drugs are generic and inexpensive, there is little incentive for the pharmaceutical industry to fund the randomized trials that would show their effectiveness definitively. We advocate that confirmation of these findings in randomized trials be considered a high research priority, as the potential impact on human lives saved could be immense.