According to Alfred Lindesmith, the critical experience in someone becoming fixated as a heroin addict is not the euphoria produced by the drug but the relief from withdrawal symptoms.

Withdrawal Symptoms

are physical or psychological effects experienced when reducing or ceasing intake of a substance that one is dependent on.

Heroin Addict

An individual suffering from addiction to heroin, a powerful illegal opioid, characterized by a compulsive need to use the drug despite harmful consequences.

Alfred Lindesmith

A sociologist known for his studies on drug addiction and for being an early critic of the US drug policy.