What is typically the first emotional reaction after a dose of heroin?

The first emotional reaction typically experienced after a dose of heroin is euphoria. Upon administration, heroin rapidly crosses the blood-brain barrier and is converted to morphine, which then binds to opioid receptors in the brain, leading to a significant release of dopamine. This results in a powerful feeling of pleasure and well-being, often described as a "rush" or euphoria.

While feelings of relief and calmness can follow in subsequent phases as the drug affects the user, the initial reaction is overwhelmingly characterized by intense euphoria. This initial high can set the stage for the highly addictive nature of heroin, as individuals often seek to replicate that initial euphoric experience, which can lead to repeated use and increased tolerance.