Strong interpersonal relationships have been shown to ward off drug addiction, and new clues as to why come from prairie voles—rodents that form long-term, monogamous bonds with their mates. Kimberly A. Young of Florida State University and her colleagues found that pair-bonded voles responded less than unattached, sexually naive voles to the rewarding properties of amphetamine. The drug boosted dopamine, a brain chemical involved in pleasure and motivation, equivalently, but pair-bonded voles had fewer receptors ready to receive the dopamine signal. Such evidence that social attachments alter the brain’s response to drugs may spur new ideas for addiction treatment.