IUPAC: (S)-N-methyl-1-phenylpropan-2-amine · MW 149.24 g/mol · CAS 537-46-2 (d-isomer) · racemate CAS 7632-10-2
N-methyl-α-methylphenethylamine. Substituted amphetamine · N-methyl homolog of amphetamine · monoamine substrate-releaser. Street names: meth, crystal, ice, glass, tina, crank, speed, shabu. Rx as Desoxyn (ADHD, obesity).
Methamphetamine is not a reuptake blocker like cocaine — it is a transporter substrate that hijacks the monoamine carriers and runs them in reverse. It is taken up through DAT, NET and SERT as if it were the neurotransmitter itself, then drives non-exocytotic efflux of dopamine, norepinephrine and (weakly) serotonin back out into the synapse down their concentration gradients. The added N-methyl group over amphetamine raises lipophilicity and CNS penetration, which — together with its long half-life — is why the subjective effects are more intense and far longer-lasting than amphetamine at equivalent transporter potency.
Methamphetamine is carried inward by DAT and NET using the same Na⁺/Cl⁻ electrochemical gradient that normally powers dopamine and norepinephrine reuptake. It competes with the native substrate and enters the terminal cytoplasm.
As a weak base and VMAT2 inhibitor (Ki ~2,460 nM), methamphetamine collapses the vesicular proton gradient, dumping stored dopamine from synaptic vesicles into the cytosol — building a large releasable cytoplasmic pool.
Elevated cytoplasmic dopamine plus transporter phosphorylation (PKC / CaMKII) switches DAT into an inward-to-outward efflux mode. Dopamine floods the synapse independent of action potentials — the core of the reward signal.
Methamphetamine activates intracellular TAAR1 (human EC₅₀ ~1,300–1,500 nM), triggering cAMP/PKA signaling that promotes DAT phosphorylation, internalization and reverse transport — TAAR1 is a positive amplifier of efflux, not a brake, in dopamine neurons.
Methamphetamine is a weak, reversible MAO inhibitor (MAO-B Ki in the high-μM range) and a poor MAO substrate, so cytoplasmic dopamine is spared from degradation — further enlarging the pool available for efflux.
At higher concentrations methamphetamine engages the sigma-1 receptor (Ki ~8,320 nM), modulating ER-mitochondrial calcium and contributing to the excitotoxic / neuro-inflammatory profile of chronic high-dose use.
The key distinction from cocaine (a pure competitive blocker) is that methamphetamine's release is substrate- and gradient-dependent: it requires transporter turnover and the Na⁺ electrochemical gradient, and it empties both vesicular and cytoplasmic stores. This produces a larger, more sustained, less self-limiting dopamine signal than reuptake blockade — a major reason the drug's reinforcing and neurotoxic potential is so high.
Methamphetamine's defining PK feature is its long elimination half-life (~9–12 h) — roughly double that of cocaine's minutes-long duration and long enough that a single dose produces 10+ hours of stimulation and days of sleep disruption. It is a weak base (pKa ~9.9), so elimination is strongly urine-pH dependent: acidic urine dramatically increases renal clearance of unchanged drug, while alkaline urine prolongs it. A substantial fraction (~30–54%) is excreted unchanged in urine.
Metabolism cascade: Two principal CYP2D6-mediated routes — aromatic hydroxylation and N-demethylation — plus direct renal excretion of unchanged drug.
Amphetamine (marked ★) is the pharmacologically active N-demethylated metabolite — itself a full monoamine releaser (see Amphetamine, #006) — so a meth dose delivers a two-stage stimulant exposure: the parent drug followed by a longer tail of active amphetamine. Roughly 4–7% of a dose appears in urine as amphetamine.
Because CYP2D6 is the primary metabolic enzyme, poor metabolizers (~7–10% of people of European descent) and anyone co-using CYP2D6 inhibitors (many SSRIs, bupropion, ritonavir) accumulate higher parent-drug exposure and are at elevated risk of cardiovascular and hyperthermic toxicity from a "normal" dose.
Unlike MDMA (serotonin-dominant) or amphetamine's more balanced profile, methamphetamine's functional signature is catecholamine-dominant: it releases norepinephrine and dopamine far more potently than serotonin (NET > DAT ≫ SERT). That biochemistry maps directly onto its clinical picture — powerful reinforcement, intense sympathetic arousal, and a serotonergic contribution that only becomes prominent at high, repeated doses.
Massive AP-independent dopamine efflux in the nucleus accumbens (NAc shell) and dorsal striatum produces the euphoria, hyperfocus and compulsive drug-seeking. Because release empties both vesicular and cytoplasmic pools and outlasts a single action-potential burst, the reward signal is larger and longer than with cocaine — a key driver of methamphetamine's exceptionally high addiction liability and rapid habit formation.
NE efflux via NET (its single most potent target) drives the sympathomimetic syndrome: tachycardia, hypertension, vasoconstriction, mydriasis, hyperthermia, appetite suppression and wakefulness. This is the axis behind the acute medical emergencies — hypertensive crisis, myocardial ischemia, arrhythmia, stroke and malignant hyperthermia — and it is dose-additive with any other sympathomimetic.
Serotonin release is comparatively weak (release EC₅₀ ~736 nM, ~30× less potent than at DAT), so meth is not an entactogen. But at high or repeated doses the combined dopamine/serotonin surge plus sleep deprivation produces the characteristic stimulant psychosis (paranoia, formication, hallucinations) and contributes — via hyperthermia, oxidative stress and glutamate excitotoxicity — to the long-lasting monoaminergic terminal damage seen in chronic users.
Sustained dopamine overflow drives downstream glutamate release in striatum and cortex; combined with hyperthermia, mitochondrial stress and microglial activation, this produces the reactive oxygen/nitrogen species and DAT/TH terminal loss documented in preclinical models and human neuroimaging. Much of the cognitive impairment of heavy chronic use maps onto this circuit, and it partially recovers with prolonged abstinence.
The behavioral end-state of high-dose bingeing ("tweaking") — hypervigilance, stereotyped repetitive behavior, paranoia and psychosis — is the predictable phenotype of days of unopposed striatal dopamine release layered on top of total sleep deprivation. It is a pharmacological state, not a moral one, and it resolves with sleep, hydration, and time.
Evidence-based, non-moralistic. These risks are dose-dependent, route-dependent, and context-dependent — and most are manageable with accurate information, pacing, and monitoring.
In the dDAT · methamphetamine complex (PDB 4XP6) the ligand sits in the S1 central site, wedged between TM1, TM3, TM6 and TM8 with its protonated amine coordinated near Asp46 and the Na⁺/Cl⁻ sites. Methamphetamine is a small, near-rigid molecule: one rotatable-bond-limited ethylamine arm and a phenyl ring. Compared with a bulky reuptake blocker like nortriptyline (the ligand in 4M48) or cocaine, it buries far less surface and freezes out far fewer rotamers on binding.
Read through a Shannon-entropy lens — the axis FlexAID∆S scores explicitly — binding is a trade between enthalpic contacts and the configurational entropy the system surrenders. A compact substrate like methamphetamine pays a small ΔSconf penalty: few ligand torsions are quenched, and critically the transporter does not get locked into a single occluded pose. That residual conformational freedom is the whole point — the carrier must still cycle through outward-open → occluded → inward-open states to translocate the substrate and, in reverse, to efflux dopamine. A high-affinity blocker instead collapses the transporter's conformational entropy, clamping it in one state and paying a large ΔS penalty for a large ΔH gain.
That distinction — modest entropy cost, preserved carrier dynamics vs. a deep entropy well that arrests the cycle — is the structural-thermodynamic restatement of "substrate-releaser vs. reuptake-blocker," and it is exactly the kind of ΔS term a docking model must get right to rank a releaser against a blocker rather than just counting contacts.
| Target | Potency | Rel. | Mechanism |
|---|---|---|---|
|
NET
Norepinephrine transporter (SLC6A2)
|
EC₅₀ = 12.3 nM
[³H]NE release
|
Substrate-releaser | |
|
DAT
Dopamine transporter (SLC6A3)
|
EC₅₀ = 24.5 nM
[³H]DA release
|
Substrate-releaser | |
|
SERT
Serotonin transporter (SLC6A4)
|
EC₅₀ = 736 nM
[³H]5-HT release
|
Weak releaser | |
|
TAAR1
Trace amine-associated receptor 1
|
EC₅₀ ≈ 1,300–1,500 nM
human TAAR1
|
Agonist | |
|
VMAT2
Vesicular monoamine transporter 2
|
Ki = 2,460 nM
rat striatal uptake
|
Inhibitor | |
|
σ1R
Sigma-1 receptor
|
Ki = 8,320 nM
|
Agonist |