5-MeO-pyr-T, also known as 5-methoxy-N,N-tetramethylenetryptamine or as 5-methoxy-3-(2-pyrrolidinoethyl)indole, is a serotonin receptor modulator and psychedelic drug of the tryptamine, 5-methoxytryptamine, and pyrrolidinylethylindole families. It is the 5-methoxy analogue of pyr-T and the derivative of 5-MeO-DMT and 5-MeO-DET in which their N,N-dialkyl groups have been cyclized into a pyrrolidine ring.

The drug acts primarily as a highly potent serotonin 5-HT_1A receptor agonist, with much lower activity at the serotonin 5-HT_2A receptor and other serotonin receptors. 5-MeO-pyr-T shows far greater selectivity for the serotonin 5-HT_1A receptor than 5-MeO-DMT.

5-MeO-pyr-T was first described in the scientific literature by 1962.

In his book TiHKAL, Alexander Shulgin gives the dose of 5-MeO-pyr-T as 0.5 to 2 mg orally and its duration as "several hours". It was also assessed at doses of 1 to 4 mg smoked.

The drug's effects were dose-dependent and variably included intense tinnitus (ear ringing), nausea and vomiting, miosis (pupil constriction), confusion or cognitive impairment, uncomfortableness, minor dysphoria, partial to complete amnesia, flailing, rolling about, quivering, and shaking, unconsciousness, and prolonged hangover. Reports of psychedelic-like effects were mixed, ranging from producing no closed-eye visuals and none of the "shifting shapes, colors and forms" of dimethyltryptamine (DMT) or the clarity or energy of 5-MeO-DMT, to producing a rush, being "intense but not terrifying", initially 5-MeO-DMT-like, ego death, full body buzz, humming resonance, and feeling that "God is love". Other notable comments included "absolute poison", "never again", "very negative", "felt as if the top of my head was blown off", user's actions being scary and others being alarmed, wandering the streets in a fugue state, and the drug being "some weird-ass shit". Its effects have also been described as "white-out" analogously to 5-MeO-DMT and with amplified amnesic effects compared to 5-MeO-DMT.

The effects of 5-MeO-pyr-T appear to be highly variable between individuals. It was described as being very different from other psychedelics and it was emphasized that a trip sitter is essential for 5-MeO-pyr-T. Shulgin has also described 5-MeO-pyr-T as being "not hallucinogenic" and instead as producing "long-lived amnesia and unconsciousness".

5-MeO-pyr-T shows very high affinity for the serotonin 5-HT_1A receptor and much lower affinity or activity at other assessed serotonin receptors. At the serotonin 5-HT_1A receptor, it had an affinity (K_i) of 0.577 nM and an activational potency (EC₅₀Tooltip half-maximal effective concentration) of 2.40 nM. These values were respectively 646-fold and 34-fold more potent than at the serotonin 5-HT_2A receptor (K_i = 373 nM, EC₅₀ = 13.5–81.3 nM (depending on assay), E_maxTooltip maximal efficacy = 92%). In other studies, it was a partial agonist of the serotonin 5-HT_2A receptor, with an EC₅₀ of 692 nM and an E_max of 73%. In addition, it was a partial agonist of the serotonin 5-HT₄ receptor in the rat esophagus, with an EC₅₀ of 355 nM and an E_max of 53%. The drug has also been predicted to bind to the serotonin 5-HT₇ receptor, with a predicted affinity (K_i) of 631 nM. In one study, relative to 5-MeO-DMT, 5-MeO-pyr-T had 12-fold greater activational potency at the serotonin 5-HT_1A receptor and 3-fold reduced activational potency at the serotonin 5-HT_2A receptor, with 38-fold increased selectivity for the serotonin 5-HT_1A receptor over the serotonin 5-HT_2A receptor.

Besides the serotonin receptors, 5-MeO-pyr-T is very weakly active at the serotonin transporter (SERT). It showed an affinity (K_i) for the SERT of 3,006 nM and an inhibitory potency (IC₅₀Tooltip half-maximal inhibitory concentration) in terms of serotonin reuptake inhibition of 2,765 nM. Additionally, 5-MeO-pyr-T is a substrate of the SERT and acts as a partial serotonin releasing agent in HEK293 cells, with an EC₅₀ of 5,700 nM.