The limbic system is a collection of brain structures that includes the hippocampus, hypothalamus and amygdala. Pleasure levels inside the limbic system are regulated by a chemical messenger (neurotransmitter) inside the brain called dopamine. Generally speaking, relatively high levels of this chemical translate into an increased experience of pleasure, while relatively low levels translate into a decreased experience of pleasure. Like most other commonly abused drugs, methamphetamine triggers euphoria by boosting the limbic system’s dopamine levels. However, while some drugs produce relatively modest dopamine increases (two to four times above normal), methamphetamine produces an extreme dopamine boost (12 to 13 times above normal). This extreme effect largely accounts for the highly addictive nature of the drug. Clip from: NIH (Video credit)