Final answer:
After intravenous heroin injection, the drug rapidly reaches the brain, causing a surge of dopamine and a euphoric rush. The effects can last for hours, but there are serious health risks associated with intravenous drug use.
Step-by-step explanation:
After a person is injected with heroin intravenously, it quickly enters the bloodstream and travels to the brain. Heroin is converted to morphine in the body, and once it reaches the brain, it binds to opioid receptors. This results in a dramatic surge of dopamine, a neurotransmitter responsible for pleasure and reward. The injection of heroin intravenously produces a quick and intense rush of euphoria, followed by a period of sedation. The effects can last for several hours. However, intravenous drug use carries significant health risks, including the potential transmission of diseases such as HIV and hepatitis.