Researchers have found that melatonin, a hormone that regulates sleep, may help reduce the side effects of tamoxifen, a common breast cancer drug. When paired with tamoxifen in lab tests, melatonin helped the drug kill cancer cells more effectively, potentially reducing the need for tamoxifen treatment and therefore its side effects. Specifically, nanostructures filled with melatonin injected several times a day were shown to help tamoxifen eliminate breast cancer cells while the melatonin breakdown products left behind caused no harm. This early-stage research presents a potential new approach to improving breast cancer treatment.