2,5-Dimethoxy-4-iodoamphetamine (DOI) is a psychedelic drug and a substituted amphetamine. Unlike other substituted amphetamines, however, it is not a stimulant. DOI has a stereocenter and R-(−)-DOI is the more active stereoisomer. In neuroscience research, [125I]-R-(−)-DOI is used as a radioligand and indicator of the presence of 5-HT2A serotonin receptors. DOI's effects have been compared to LSD, although there are differences that experienced users can distinguish. Besides the longer duration, the trip tends to be more energetic than an LSD trip, with more body load and a different subjective visual experience. The after effects include residual stimulation and difficulty sleeping, which, depending on the dose, may persist for days. While rare, it is sometimes sold as a substitute for LSD, or even sold falsely as LSD, which may be dangerous because DOI does not have the same established safety profile as LSD.