Results from a new clinical trial suggest that a group of brain regions known as the 'salience network' is activated after a drug is taken intravenously, but not when that same drug is taken orally. When drugs enter the brain quickly, such as through injection or smoking, they are more addictive than when they enter the brain more slowly, such as when they are taken orally. However, the brain circuits underlying these differences are not well understood. This study offers new information that helps explain what may be causing this difference.