Research chemicalStimulantResearch chemicalPhenidateDopamine reuptake inhibitor

Methylnaphthidate (HDMP-28)

Also known as HDMP-28 · methylnaphthidate · naphthylphenidate

Written by enwyReviewed 4 Aug 20262 sources0 comments

Methylnaphthidate (HDMP-28) is a naphthyl analogue of methylphenidate in which the phenyl ring is replaced by a naphthalene ring. It is a potent dopamine reuptake inhibitor stimulant sold as a research chemical, with essentially no human safety data.

01 Overview

Methylnaphthidate, also known as HDMP-28, replaces the phenyl group of methylphenidate with a naphthyl group, producing a potent dopamine reuptake inhibitor. It appeared as a designer stimulant alongside other phenidate analogues.

Human data is limited to anecdote; the compound is characterised mainly through in vitro transporter studies. Its potency and dopaminergic action suggest significant abuse and cardiovascular risk, but these remain unconfirmed in humans.

02 Mechanism

Potent inhibitor of the dopamine (and noradrenaline) transporter; the naphthyl ring increases affinity and dopaminergic potency relative to methylphenidate.

03 Dosing

Tier	Dose	Route	Notes
Light	3–8 mg	Oral	Anecdotal; considered potent, so doses are small.
Common	3–12 mg	Insufflated	Faster onset; strong compulsive redosing risk.
Common	8–20 mg	Oral	Strong dopaminergic stimulation; high redosing potential.

04 Effects

Effect	Magnitude	Evidence
Appetite suppressionReduced hunger during the active period.		Anecdotal
Strong stimulationMarked energy, drive and wakefulness from potent dopamine reuptake inhibition.	strong	Anecdotal
EuphoriaPronounced dopaminergic euphoria, contributing to abuse potential.		Anecdotal

05 Side effects

Effect	Severity	Frequency	Evidence
Insomnia and comedownSleep loss followed by fatigue, low mood and irritability.	Moderate	Very common	Anecdotal
Compulsive redosingPotent dopaminergic reinforcement drives binge dosing and escalation.	Severe	Very common	Anecdotal
Cardiovascular strainTachycardia and hypertension; risk amplified by potency and redosing.	Severe	Common	Unconfirmed

06 Legal status

Psychoactive Substances Act 2016

Production and supply prohibited. · as of Jan 2026

United States

Not federally scheduled by name

Possible analogue under the Federal Analogue Act. · as of Jan 2026

07 References

HDMP-28 (methylnaphthidate) transporter pharmacologyPubMed

New psychoactive substances overviewEUDA (European Union Drugs Agency)

08 Discussion0 comments

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This page is reference information, not medical advice. Doses and protocols are documented as they appear in the clinical literature and in practice — describing them is not a recommendation to use them. Countermeasures listed here are not a substitute for a physician. Legal status varies by jurisdiction and changes.