Leonard is a heroin addict. He is very careful about overdosing and only buys his drug from pushers known to him (to avoid a "bad" batch). He typically shoots up in his basement apartment, but is now at a friend's house and needs a fix really badly. He's never done drugs at his friend's house before, but he's desperate. He injects his normal "safe" dosage of heroin but almost dies of an overdose. What happened?

The effect of the heroin was increased because Leonard injected it in a strange environment and his body could not use the stimuli in his basement to prepare for it.

In Psychology, the theory of classical conditioning explains this better which is defined as a learning process in which a previously neutral stimulus (such as a bell) is paired with a potent stimulus (such as food in the case of a dog), so that the neutral stimulus comes to elicit a conditioned response (salivation) similar to the one elicited by the potent stimulus.

send them to therapy or somthing like that