Demand for heroin in rats: effects of non-drug alternative substitutes and complements.

Summary: Why do people or animals keep using drugs even when it gets hard to get them? Scientists looked at rats to see what makes them want heroin more or less. They found that if rats had other options—like a safe break (a "timeout") or cheaper heroin—they worked less for the expensive heroin. These other options acted like "substitutes."

But, when female rats were given sweet water (saccharin) along with heroin, they actually wanted the heroin more. The sweet water acted like a "complement" that made the drug even better for them. This shows that having other choices can either help lower drug use or accidentally make it worse, depending on what the choice is!