So, why do we experience a "contact high?" And, if placebos work even if you don't believe in them, do those who have never used marijuana or don't believe in a "contact high" still experience a "contact high"? The answer is surely a complicated mix of evolutionary and epigenetic factors that we don't fully understand, but it is probably very closely related to the biological mechanisms that underlie placebo effects. Experienced users are probably experiencing effects related to conditioning and coupling. The similar environment, people, and smells will subconsciously evoke similar but relatively muted responses. Even those who have never used marijuana, may "feel" somewhat similar to those around them. If everyone is laughing, smiling, and feeling happy, then you will too. Ever hang around a depressed person? Yeah, it's depressing. It is also possible that mirror neurons play a role in the subconscious mimicking of the behavior of those around us. So if you are worried about that upcoming drug test and your "contact high," don't be, it's all in your head.