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Methylnaphthidate Facts

Stimulant; Phenidate; Dopamine reuptake inhibitor

Description

HDMP-28 (methylnaphthidate) is a synthetic stimulant of the substituted phenidate class. It blocks the recycling of dopamine, norepinephrine, and serotonin in the brain, amplifying all three signals simultaneously.[1]

Subjective effects include stimulation, wakefulness, appetite suppression, and mood elevation. The experience resembles Methylphenidate but may carry a warmer emotional tone — attributed to serotonin activity, though this has not been confirmed in controlled study.[2]

Psychological dependence potential is high — animal studies show reinforcement equal to cocaine[3] — and the cardiovascular system bears the main acute toxicity burden. Serotonin activity adds interaction risks absent from Methylphenidate; combining with serotonin-raising drugs or MAOIs can trigger a life-threatening overheating and seizure response.[1]

Dose and durationby route · individual sensitivity varies

Oral(mg)
Threshold< 4 mgLight10 – 15 mgCommon15 – 30 mgStrong30 – 50 mgHeavy50+ mg

Starts in 1 – 10 minLasts 2 – 5 hoursAfter-effects 1 – 8 hours

Body and dependence

Acute toxicity
Moderate
Chronic toxicity
Moderate
Physical dependence
Negligible
Psychological dependence
High
Withdrawal
Mild
Compulsive redosing
High

Tolerance

Builds
Moderate
Fully resets after
10 days
Carries over to
methylphenidate; ethylphenidate; isopropylphenidate; cocaine

Effectslikely at a common dose

Perception
none likely · 6 possible
Body
Appetite suppression; Pupil dilation; Stimulation; Wakefulness; +18 possible, including Insomnia, Vasoconstriction, Muscle tension
Thinking
none likely · 19 possible, including Compulsive redosing urge, Cognitive dysphoria
Feeling
none likely · 7 possible, including Anxiety, Anhedonia, Depression
Self
none likely · 7 possible, including Craving, Ego inflation
Time
none likely · 2 possible
Awareness
Sustained attention (vicara); +2 possible

Who shouldn't take it

Absolute
Pre-existing cardiovascular disease; MAOI use
Relative
Seizure disorders; History of psychosis or bipolar disorder; Concurrent serotonergic medication (SSRIs, SNRIs, triptans)

Combinations64 recorded

Lethal (4)
Cocaine; Ibogaine; MDMA; Tramadol
Dangerous (29)
Alpha-2 adrenergic receptor antagonist; Amphetamines; Benzodiazepines, Barbiturates; Ephedrine, Pseudoephedrine; Local anesthetics; MAOIs; MDMA, Amphetamines; MDMA, MDA; NDRIs (Wellbutrin); NRIs; Opioids; SSRIs; Stimulants; Anticholinergics; Antipsychotics; Buspirone; Caffeine; Dopamine agonists; DXM; GHB, Baclofen; GHB, GBL; Ketamine, DXM, PCP; Lithium; NSAIDs; and 5 more, see full page
Caution (28)
See full page: psychedex.org/substances/methylnaphthidate
Not graded (3)
Not listed never means safe.

Seek help immediately if

  • Chest pain; racing, pounding, or irregular heartbeat
  • Very high body temperature; heavy sweating; hot, flushed skin
  • Severe agitation, paranoia, panic, or confusion
  • Severe headache; muscle rigidity or twitching
  • Seizures
  • Signs of stroke — face drooping, one-sided weakness, slurred speech
  • Difficulty breathing; collapse or unconsciousness

What to do

  1. Call emergency services for chest pain, overheating, seizure, or unresponsiveness
  2. Move them to a cool, quiet place and reduce stimulation
  3. Cool the body — remove excess clothing, apply cool damp cloths, fan them
  4. Keep them calm; reassure — panic worsens the cardiovascular strain
  5. If seizing, protect from injury (don't restrain); recovery position afterward
  6. Monitor breathing and be ready to give rescue breaths / CPR

Most stimulant overdoses settle with cooling, a calm environment, and time. The medical danger is hyperthermia, cardiac events (arrhythmia, heart attack, stroke), and seizures — get help immediately if any appear.

988 Suicide & Crisis LifelineFireside Project: 62-FIRESIDE

Version r1.a1 · Not medical advice

References

  1. [1]
    ^abHandWiki contributors (2023) Methylnaphthidate (HDMP-28) - HandWiki Chemistry Link
  2. [2]
    ^Anonymous blogger (novelpsychs.wordpress.com) (2015) Novel Psychoactive Substances Blog - HDMP-28/Methylnaphthidate Link
  3. [3]
    ^Lile JA, Wang Z, Woolverton WL, France JE, Gregg TC, Davies HM, Nader MA (2003) The reinforcing efficacy of psychostimulants in rhesus monkeys: the role of pharmacokinetics and pharmacodynamics — Journal of Pharmacology and Experimental Therapeutics PMID:12954808
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