IUPAC: (RS)-1-phenylpropan-2-amine · MW 135.21 g/mol · CAS 300-62-5
α-methylphenethylamine. Phenethylamine · substituted amphetamine · MDXX entactogen/empathogen. Street names: Ecstasy, Molly, X, E, Mandy, Amphetamine, Mitsubishi.
Amphetamine is not a classic reuptake inhibitor — it is a transporter substrate that triggers carrier-mediated efflux, the exact inverse of how cocaine works. Where cocaine physically blocks the transporter pore, Amphetamine rides DAT inward and hijacks the transporter's alternating-access cycle to run it in reverse, flooding the synapse with serotonin.
Amphetamine enters the serotonergic terminal as a transported substrate via DAT, exploiting the inward Na⁺/Cl⁻ gradient. This is the same route used by 5-HT itself.
Amphetamine inhibits VMAT2 (Ki ~6,400 nM) and collapses the vesicular ΔpH, releasing stored 5-HT into the cytoplasm where it is available for efflux.
Amphetamine activates CaMKII, which phosphorylates DAT at Thr-616 and Ser-277, switching the transporter from reuptake mode to efflux mode — forcing 5-HT out down its concentration gradient.
Amphetamine similarly traverses NET (Ki 168 nM) and DAT (Ki 1,090 nM), causing norepinephrine and dopamine efflux — though with far lower efficiency than at DAT.
At higher concentrations, Amphetamine is a low-affinity partial agonist at 5-HT₂A (Ki 2,300 nM) and 5-HT₂B (Ki 480 nM). The 2B agonism is a cardiac liability with chronic exposure.
Amphetamine is a TAAR1 agonist (EC₅₀ ~1,600 nM), which activates inhibitory presynaptic autoreceptors and provides a negative-feedback brake on dopamine and serotonin release.
The key distinction from cocaine (a pure blocker) is that Amphetamine's serotonin release is exchange-diffusion dependent: it requires the Na⁺ electrochemical gradient and is blocked by Na⁺ channel blockers. At the S1 central binding site of DAT, Amphetamine occupies the same orthosteric pocket as SSRIs and cocaine analogs, but its substrate kinetics direct the transporter into an outward-facing inversion state rather than competitive occlusion.
Amphetamine exhibits nonlinear, dose-dependent pharmacokinetics because it is a mechanism-based inhibitor of CYP2D6 — its own primary metabolic enzyme. At recreational doses, CYP2D6 is substantially inhibited after the first dose, meaning plasma exposure increases disproportionately on re-dosing. This self-inhibition mechanism underlies the "second pill doesn't work the same way" phenomenon and explains the steep danger curve at high doses.
Metabolism cascade: Two parallel pathways converge on catechol intermediates that are then methylated by COMT.
MDA (3,4-methylenedioxyamphetamine, marked ★) is pharmacologically active — it retains ~40% of Amphetamine's DAT potency and contributes meaningfully to the experience, particularly the more psychedelic-tinged later phase given its longer half-life (16–38 h). CYP2D6 poor metabolizers (PMs, ~7–10% of Europeans) have dramatically elevated Amphetamine exposure and are at substantially higher risk of serotonin toxicity and hyperthermia from standard doses.
HHMA (3,4-dihydroxymethamphetamine) and HMA (4-hydroxy-3-methoxymethamphetamine) are the primary urinary metabolites and are what drug tests typically detect via immunoassay cross-reactivity. Both are pharmacologically weak at the major targets.
The pharmacological cascade initiated by Amphetamine at the transporter level translates into distinct, anatomically specific circuit effects. The disproportionate DAT selectivity (DAT:NET:DAT ≈ 30:6:1 at therapeutic doses) makes Amphetamine uniquely serotonergic relative to classical amphetamines, which is the biochemical basis of its entactogenic profile.
Massive 5-HT release in the limbic system — particularly the amygdala, insula, anterior cingulate cortex (ACC), and mPFC — drives the signature prosocial effects. 5-HT in the mPFC potently inhibits fear circuitry (BLA→CeA), enabling extinction of threat-conditioned responses. This is the mechanism underlying Amphetamine's utility in PTSD-assisted therapy. Simultaneously, 5-HT₁A activation in the paraventricular nucleus (PVN) triggers oxytocin release.
Dopamine release via DAT substrate activity in the nucleus accumbens (NAc shell > core) mediates the hedonic and motivational components — euphoria, locomotor activation, and reward salience. The DA surge is substantially smaller than with amphetamine (which has the opposite DAT:DAT selectivity), explaining why Amphetamine produces less compulsive redosing and addiction potential than classical stimulants, though the risk is not zero.
NE efflux via NET in the locus coeruleus (LC) projection fields drives sympathomimetic effects: tachycardia, hypertension, hyperthermia, pupillary dilation, dry mouth, and the "jaw clenching" (bruxism, likely via NE + 5-HT at the trigeminal motor nucleus). These SNS effects are the primary medical concern: hyperthermia in hot/crowded environments is the leading cause of Amphetamine fatality.
5-HT₁A agonism in the hypothalamic PVN stimulates oxytocin (OXT) secretion into blood and brain. Elevated CNS oxytocin acts at the BNST and lateral septum to suppress social anxiety and enhance social reward. This neuromodulatory effect is largely independent of direct DA reward and is why Amphetamine empathy persists even when dopaminergic effects plateau — the prosocial window extends well past peak stimulant effects.
At very high doses or with repeated dosing, 5-HT₂A partial agonism becomes more pharmacologically relevant, contributing mild perceptual distortions — closed-eye visuals, heightened sensory processing — that gives Amphetamine its mild psychedelic fringe. This is mechanistically distinct from psilocybin/LSD (which are full 5-HT₂A agonists) and is not the primary driver of the Amphetamine experience.
Evidence-based, non-moralistic. These risks are dose-dependent, context-dependent, and manageable with accurate information.
| Target | Affinity | Rel. | Mechanism |
|---|---|---|---|
|
DAT
Serotonin transporter (SLC6A4)
|
Ki = ~1,400 nM
EC₅₀ 74 nM (efflux)
|
Substrate-releaser | |
|
NET
Norepinephrine transporter (SLC6A2)
|
Ki = 168 nM
EC₅₀ 94 nM (efflux)
|
Substrate-releaser | |
|
DAT
Dopamine transporter (SLC6A3)
|
Ki = 1,090 nM
EC₅₀ 278 nM (efflux)
|
Substrate-releaser | |
|
5-HT₂B
Serotonin 2B receptor
|
Ki = 480 nM
|
Agonist | |
|
σ1R
Sigma-1 receptor
|
Ki = 2,560 nM
|
Agonist | |
|
5-HT₂A
Serotonin 2A receptor
|
Ki = 2,300 nM
|
Partial agonist | |
|
TAAR1
Trace amine-associated receptor 1
|
EC₅₀ ≈ 1,600 nM
|
Agonist | |
|
α₂-AR
α₂ Adrenergic receptor
|
Ki = 4,100 nM
|
Agonist | |
|
VMAT2
Vesicular monoamine transporter 2
|
Ki = 6,400 nM
|
Inhibitor |