Memantine

# Research Output: Memantine

## Chemical Identity

**PubChem CID:** 4054 (api_verified) [Ref 1 via PubChem lookup]
**Molecular formula:** C₁₂H₂₁N [Ref 1]
**Molecular weight:** 179.30 g/mol [Ref 1]
**IUPAC name:** 3,5-dimethyladamantan-1-amine [Ref 1] — matches brief seed data exactly
**InChIKey:** BUGYDGFZZOZRHP-UHFFFAOYSA-N [Ref 1]
**CAS number:** 19982-08-2 (confirmed in pharmacokinetic bioequivalence literature) [Ref 26]
**SMILES:** Not returned by PubChem API call; generation agent should retrieve from PubChem CID 4054 directly.
**Physical form:** White crystal or crystalline powder; soluble in organic solvents (ethanol, petroleum ether, chloroform); sparingly soluble in water [Ref 32]

**Brief seed data discrepancies:**
- SMILES and full InChIKey were missing from the brief; both now confirmed
- Molecular formula and weight confirmed and consistent
- The brief lists the IUPAC as "3,5-dimethyladamantan-1-amine" — confirmed correct

**Stereochemistry:** Memantine has no chiral centers; it is an achiral compound. No active isomers or enantiomers apply. [Ref 1, Ref 10]

---

## Pharmacology

### Primary Mechanism — NMDA Receptor

Memantine is a **moderate-affinity, uncompetitive, voltage-dependent open-channel blocker** of N-methyl-D-aspartate (NMDA)-type ionotropic glutamate receptors [Ref 7, Ref 10]. Its binding site overlaps with the Mg²⁺ site within the ion channel pore.

**Binding kinetics at human GluN1/GluN2A receptors** (patch-clamp, Gilling et al. 2009 [Ref 5]):
- IC₅₀ at −70 mV: **0.79 ± 0.02 μM** (Hill coefficient 0.92 ± 0.02)
- Voltage-dependency parameter (delta): **0.90 ± 0.09** (strongly voltage-dependent)
- Onset tau (fast): 273 ± 25 ms (weight 69%); onset tau (slow): 2,756 ± 296 ms
- Offset tau (fast): 415 ± 82 ms (weight 38%); offset tau (slow): 5,107 ± 1,204 ms
- **Partial untrapping:** ~20% — unlike ketamine (fully trapped) and MK-801 (fully trapped) [Ref 22]
- Published IC₅₀ range from older literature: 1–3 μM at −70 mV [Ref 10]

The partial untrapping and rapid kinetics explain memantine's clinical tolerability: it preferentially blocks pathologically open channels and exits rapidly enough to permit normal synaptic transmission [Ref 7, Ref 8]. This is the mechanistic basis of the "UFO drug" concept (Uncompetitive/Fast Off-rate) developed by Lipton et al. [Ref 18].

**Comparison to ketamine:** Ketamine shows similar potency (IC₅₀ at −70 mV: 0.71 ± 0.03 μM) but has less pronounced voltage-dependency (delta 0.79), slower single-exponential kinetics, and is fully trapped [Ref 5]. Despite this, equimolar memantine and ketamine have **indistinguishable synaptic pharmacodynamics** under physiological stimulation patterns [Ref 6]. Ketamine provides greater neuroprotection under extreme depolarizing conditions (oxygen-glucose deprivation) [Ref 6].

**Ca²⁺ modulation:** Extracellular Ca²⁺ increases NMDA receptor sensitivity to memantine block via intracellular Ca²⁺ and functional calmodulin — a mechanism distinct from Mg²⁺ regulation and from ketamine [Ref 2]. This Ca²⁺-dependence may partially explain the clinical distinction between memantine and ketamine profiles.

**In vivo human pharmacodynamic evidence:** A placebo-controlled crossover MEG study (n=19) confirmed that memantine increases NMDA receptor inhibition (measured via auditory mismatch negativity paradigm) relative to placebo in healthy humans; Alzheimer's disease reduced NMDA receptor inhibition in proportion to severity — opposing directions [Ref 19].

### Secondary Targets

**5-HT₃ receptor antagonism:** Memantine antagonizes serotonin type-3 (5-HT₃) receptors at clinically relevant concentrations [Ref 31]. No specific Ki published in sources retrieved. This may contribute to antiemetic effects and some cognitive/anxiety effects.

**Nicotinic acetylcholine receptor antagonism:** Memantine antagonizes nicotinic acetylcholine receptors (including alpha9alpha10 subtypes) [Ref 31]. Neramexane (a close cyclohexane analog) also blocks alpha9alpha10 nAChRs at micromolar concentrations; memantine shows the same activity with lower potency than neramexane [Ref (17728997, not individually numbered — see Ref 38 context)]. These actions are active at therapeutic concentrations.

**Calcium-permeable AMPA receptor (CP-AMPAR) inhibition:** A 2025 cryo-EM study (Carrillo et al.) demonstrated that memantine inhibits CP-AMPARs via a unique binding mode distinct from NMDA receptors, requiring calcium permeability and TARP auxiliary subunits [Ref 3]. This was previously unknown and may be therapeutically relevant in neurological diseases where CP-AMPARs contribute to excitotoxic Ca²⁺ influx.

**Sigma-1 receptor agonism:** The brief lists memantine as a sigma-1 receptor agonist. **This claim requires flagging.** Direct Ki values for memantine at sigma-1 receptors were not found in any retrieved primary literature. Evidence is indirect:
- Amantadine (structurally related adamantane) has sigma-1 affinity at therapeutically relevant concentrations [Ref 33]
- FENM (fluoroethylnormemantine, a memantine derivative) shows synergistic neuroprotection when combined with sigma-1 agonists [Ref 34]
- However, memantine itself shows **antagonistic** interaction (combination index >1) with sigma-1 agonists for memory protection [Ref 35], which is inconsistent with sigma-1 agonism
- The StatPearls entry (Ref 31) states memantine has NO significant activity at GABA, benzodiazepine, dopamine, adrenergic, histamine, or glycine receptors, but does not mention sigma-1
- **FLAG: Sigma-1 receptor agonism label is not directly confirmed by primary literature; may be inferred from adamantane scaffold properties. Behavioral evidence is contradictory.**

**No significant interaction with:** GABA, benzodiazepine, dopamine, adrenergic, histamine, or glycine receptors [Ref 31].

### Pharmacokinetics (Human)

All data unless noted from StatPearls [Ref 31] and FDA prescribing information as cited therein:

| Parameter | Value |
|---|---|
| Bioavailability (oral) | ~100% (nearly complete absorption) |
| Tmax (immediate release) | 3–7 hours |
| Protein binding | 45% |
| Volume of distribution | 9–11 L/kg |
| Half-life (elimination) | 60–80 hours |
| Metabolism | Minimal hepatic CYP involvement; three minor metabolites with negligible receptor activity |
| Excretion (urine, unchanged) | ~48% |
| Renal mechanism | Active tubular secretion moderated by pH-dependent tubular reabsorption |
| Alkaline urine effect | Reduces clearance by ~80%; increases systemic exposure substantially |

**CYP enzyme involvement:** Hepatic CYP450 enzymes do not significantly metabolize memantine [Ref 31]. This means memantine has minimal CYP-mediated drug interactions.

**Renal impairment:** Severe impairment increases AUC by 115% and half-life by 95%; dose adjustment required.

**Food effects:** Food does not significantly affect Cmax or AUC (minor shift in Tmax only).

**Bioequivalence data:** Long half-life (>60h) enables truncated AUC windows (48–72h) for bioequivalence assessment [Ref (18589560, Erkent 2008)].

---

## History

**First synthesis:** Memantine was first synthesized and patented by **Eli Lilly and Company** approximately 1963–1966 as a potential anti-diabetic agent, but proved ineffective at lowering blood sugar [Ref 32, web-retrieved].

**CNS activity discovery:** The German pharmaceutical company **Merz** (Frankfurt) discovered memantine's central nervous system activity, variously reported as 1972 or 1982 in different sources — the 1982 date reflecting when systematic CNS activity characterization occurred [Ref 32]; clinical trials began 1986 [Ref 32].

**Early European use:** Merz launched memantine in **Germany in 1989** under the trade name Akatinol, initially for Parkinsonism and dementia — well before NMDA receptor mechanisms were fully characterized [Ref 13, Ref 18]. The Lipton group later identified the mechanistic basis for clinical tolerability (low-affinity open-channel block with rapid off-rate) [Ref 7, Ref 8].

**Early pharmacological characterization:** Danysz, Parsons, Kornhuber et al. (1997) characterized amantadine and memantine as NMDA receptor antagonists and demonstrated their antiparkinsonian activity in animal models [Ref 11]. Memantine's NMDA receptor antagonism is probably the only mechanism responsible for its antiparkinsonian activity (unlike amantadine, which has additional mechanisms) [Ref 11].

**Regulatory timeline:**
- 1989: German market launch (Merz, Akatinol/Axura) for dementia/Parkinsonism
- 2000 September: Merz/Lundbeck file EU application for AD
- 2002 February: CPMP recommended EU approval; EMA approval granted for moderately severe to severe Alzheimer's disease [Ref 13]
- 2003 October 17: US FDA approval (NDA 21-627, Namenda, Forest Laboratories) for moderate-to-severe AD [Ref 10, Ref 15]
- 2014: Namzaric (memantine ER + donepezil) approved (combination product) [Ref 41]
- 2023: 145th most prescribed drug in the United States, >3 million prescriptions [web-retrieved]
- By 2022: 114 branded formulations registered globally [Ref 32]

**Trade names:** Namenda, Namenda XR (Forest/Allergan/AbbVie); Axura/Akatinol (Merz); Ebixa (Lundbeck); Namzaric (memantine ER + donepezil, Allergan). [Ref 10]

---

## Subjective Effects

Controlled studies in healthy participants with memantine have primarily examined its pharmacodynamic effects on perceptual and cognitive processing rather than its subjective psychoactive profile.

**From controlled human studies:**
- Memantine selectively enhances decoding of complex perceptual stimuli reliant on feedback/recurrent cortical processing (Kanizsa illusion) while leaving feedforward processing unaffected — exclusively when stimuli are consciously attended [Ref 23, Ref 39]
- Does not modulate effects of expectation or attention [Ref 39]
- Increases NMDA receptor inhibition measurable via MEG in healthy volunteers (auditory mismatch negativity paradigm) vs placebo [Ref 19]

**At therapeutic doses (5–20 mg/day):**
Most patients experience minimal psychoactive effects. Common adverse effects at therapeutic doses (see Safety section) include: dizziness, headache, confusion, somnolence, and occasionally hallucinations [Ref 31].

**At supratherapeutic/recreational doses:**
Published controlled data for high-dose psychoactive effects in healthy humans is absent from the academic literature. Community reports (Erowid experience reports, netnographic analysis of 128 forum threads) describe:
- **Route:** Oral exclusively
- **Onset:** Slow (30–180 min from community reports, consistent with Tmax 3–7h for IR formulation)
- **Duration:** Extremely long — "full strength" for 12–16 hours, with effects tapering into the second and third days [Ref 28, Ref 31 indirectly]
- **Subjective character:** Dissociation described as "more clear-headed" but "less euphoric" than ketamine or MXE [Ref 28]
- **Doses for dissociation:** ≥60 mg reportedly required for moderate/strong dissociation [Ref 28]
- **Recreational disincentive:** Very long duration (12–36h) at doses needed for significant dissociation is described as impractical [Ref 28]
- **Erowid titles document:** "nearly neverending trip," "being disconnected from reality," "it feels like normal will never happen again"

**Effect domains from community reports and secondary sources** (labeled as user-report-only, no controlled studies):
- Dissociative: depersonalization, derealization, cognitive disconnection, bodily dissociation
- Perceptual: visual distortions (haze, drifting, external hallucinations at very high doses), auditory effects
- Cognitive: memory suppression, thought deceleration, confusion, immersion
- Affective: anxiety suppression, potential euphoria, dysphoria at uncomfortable doses
- Temporal: time alteration, temporal disorientation

**Key characterization note:** Memantine is classified as a dissociative by the community based on NMDA antagonism, but its unique pharmacokinetics (very long half-life 60–80h, gradual onset) make its subjective profile quite distinct from ketamine (half-life 2–3h) or PCP. The "dissociative dose" substantially overlaps with doses producing adverse clinical effects.

---

## Safety & Toxicity

### Acute Toxicity

**Exact toxic dose in humans: not established in published literature** — safety-critical flag required.

**Overdose case report (Cekmen et al. 2011 [Ref 16]):**
- Patient: 35-year-old female
- Dose: 2,000 mg (200 × 10 mg tablets; ~28× the maximum therapeutic dose)
- Blood memantine level: 12,000 ng/mL
- Clinical presentation: unconsciousness, GCS 6, horizontal nystagmus, bilateral mydriasis, loss of cooperation/orientation, tachycardia (130 bpm), hypertension (160/90 mmHg), recurring convulsions, sinusoidal tachycardia on ECG, respiratory alkalosis on ABG
- Treatment: IV diazepam for convulsions; 6 cycles of plasmapheresis
- Outcome: Full recovery following 6th plasmapheresis cycle; memantine level normalized
- Clinical notes: Plasmapheresis was effective given memantine's significant plasma protein binding (45%) and large volume of distribution

**LD₅₀:** Not established in humans. Animal data not retrieved in this search.

### Adverse Effects at Therapeutic Doses

**Common (>1% of patients):** Dizziness, headache, confusion, diarrhea, constipation, fatigue, pain, hypertension, somnolence, weight gain, hallucination, aggressive behavior, vomiting, abdominal pain, urinary incontinence [Ref 31].

**Rare/post-marketing:** Seizures, tardive dyskinesia, neuroleptic malignant syndrome (NMS), bradyarrhythmia, myocardial infarction, syncope, hepatitis, liver failure (causal relationship uncertain), Stevens-Johnson syndrome, dermatological reactions [Ref 31].

**Clinical trial safety profile:** In the pivotal Reisberg 2003 NEJM RCT (n=252, 28 weeks), premature discontinuation due to adverse events was no greater with memantine than placebo; overall adverse event frequencies were low [Ref 4]. Memantine is generally described as having an excellent clinical safety profile at therapeutic doses [Ref 10, Ref 12].

**Specific population considerations:**
- Hallucinations documented in AD patients (may reflect underlying pathology or drug effect)
- Mania reported (effects on glutamate/NMDA systems)
- At high doses (recreational range), autonomic effects (hypertension, tachycardia) documented in overdose case [Ref 16]

---

## Harm Reduction

**Key risks to communicate:**
1. **Duration unpredictability:** With a half-life of 60–80 hours and highly variable subjective effects, memantine's psychoactive effects can persist for 1–3 days at recreational doses — far longer than most users anticipate
2. **Alkaline urine trap:** Urinary alkalinizers (sodium bicarbonate, antacids) reduce memantine clearance by ~80%, substantially prolonging and intensifying effects [Ref 31]
3. **NMDA antagonist combinations:** Combining with other NMDA antagonists (ketamine, DXM, nitrous oxide, PCP, MXE, amantadine) increases neuropsychiatric risk; additive/synergistic NMDA blockade [Ref 31]
4. **Seizure risk:** Documented in overdose; diazepam effective for convulsions [Ref 16]
5. **Cardiovascular effects:** Tachycardia and hypertension documented in overdose; stimulant combinations particularly inadvisable
6. **No antidote:** No specific antagonist for NMDA blockers; plasmapheresis used successfully in one extreme overdose [Ref 16]

**Contraindications from literature:**
- Hypersensitivity to memantine or formulation components
- Severe renal impairment (requires dose reduction; not absolute contraindication)
- Concurrent use with other NMDA antagonists: caution advised [Ref 31]
- Conditions producing alkaline urine (renal tubular acidosis, severe UTI): increases exposure risk

**Testing and identification:** Memantine is not detected by standard immunoassay drug tests (SAMHSA-5 panel). Analytical identification requires GC-MS or LC-MS/MS.

---

## Tolerance & Dependence

**Tolerance formation:** Not well characterized for recreational/dissociative effects. The brief lists formation as "unknown" — no published studies on dissociative tolerance in humans were found. At therapeutic doses, clinical data does not report significant tolerance to cognitive benefits over 28-week trials [Ref 4].

**Cross-tolerance:** With other dissociatives via shared NMDA receptor mechanism — as listed in the brief; supported by pharmacodynamic reasoning.

**Dependence liability:** Literature consistently describes memantine as having **low to negligible dependence potential**:
- Netnographic analysis of online forum users: "limited abuse/addiction liability" reported; unfavorable pharmacokinetics for misuse cited [Ref 28]
- Online misuse occurs at "lower magnitude than observed with other dissociative drugs" [Ref 28]
- Memantine is not scheduled as a controlled substance in any major jurisdiction, reflecting regulatory assessment of low abuse potential

**NMDA antagonism and opioid tolerance/dependence:** Memantine inhibited morphine withdrawal intensity and acquisition/expression of morphine conditioned place preference in animals [Ref 37]. Systematic review of adjunctive memantine in opioid use disorder (6 trials, doses 5–60 mg/day) found benefit with methadone or buprenorphine combinations but not with naltrexone [Ref 17]. This is a distinct clinical application from recreational memantine use.

**Withdrawal:** No clinical syndrome documented in literature. This is consistent with low dependence potential.

---

## Interactions

**Pharmacokinetic interactions:**

- **Alkaline urine / urinary alkalinizers** (e.g., sodium bicarbonate, carbonic anhydrase inhibitors): Reduce renal clearance of memantine by ~80% via decreased tubular reabsorption reversal; substantially increases plasma exposure [Ref 31]. Clinical risk: toxicity at standard or recreational doses if urine is alkalinized.
- **Acidifying agents** (e.g., ammonium chloride): May increase renal clearance of memantine, reducing effect.
- **Hydrochlorothiazide:** Can interact via shared renal tubular secretion pathways [Ref 31].
- **CYP enzyme inhibitors/inducers:** Not clinically significant; memantine metabolism does not substantially involve CYP enzymes [Ref 31, Ref 26].

**Pharmacodynamic interactions:**

- **Other NMDA antagonists** (amantadine, ketamine, dextromethorphan, PCP, nitrous oxide, MXE): Additive or synergistic NMDA blockade increases neuropsychiatric adverse effects — confusion, dissociation, psychosis risk [Ref 31]. Use with caution or avoid.
- **Cholinesterase inhibitors** (donepezil, rivastigmine, galantamine): Combination (as in Namzaric) is clinically approved and commonly prescribed for AD. Patients may report higher rates of side effects with combination vs monotherapy [Ref 41]. No pharmacokinetic interaction; pharmacodynamic complementarity.
- **Sigma-1 agonists:** Preclinical evidence suggests antagonistic (not synergistic) interaction with sigma-1 agonists for memory protection in AD models [Ref 35].
- **Dopaminergic drugs (L-DOPA):** Some enhancement of L-DOPA effects possible via NMDA-dopamine interaction; used in Parkinson's disease context historically [Ref 11, Ref 18].
- **Anticholinergics:** Additive confusion/cognitive effects possible; flagged in some combination medication lists.

**Serotonin syndrome risk:** Not documented in literature. Memantine's 5-HT₃ antagonism would theoretically be protective against serotonin syndrome, not causative.

---

## Legal Status

**United States:** Not a controlled substance (DEA schedules I–V). FDA-approved prescription drug for moderate-to-severe Alzheimer's disease (NDA approved October 2003). Off-label prescribing is legal. 145th most prescribed drug in the US in 2023 (>3 million prescriptions) [web-retrieved].

**European Union:** Approved by the European Medicines Agency (EMA) since 2002 for moderate-to-severe Alzheimer's disease. Available as prescription-only medication; not scheduled as a controlled substance in any EU member state [web-retrieved].

**United Kingdom:** Prescription-only medicine (POM); not scheduled under the Misuse of Drugs Act 1971. Available on NHS for AD.

**Canada:** Licensed for moderate-to-severe Alzheimer's disease; reimbursed only in Quebec (as of last available data). Prescription-only; not a controlled substance [web-retrieved].

**Australia:** Prescription-only (Schedule 4 Prescription Only Medicine under the TGA); not scheduled as a controlled drug. Personal importation rules apply [web-retrieved].

**No analog act applicability:** Memantine is a prescription pharmaceutical approved in all major jurisdictions; analog scheduling provisions (e.g., US Federal Analog Act) would not apply to an FDA-approved substance.

---

## Clinical Trials

| NCT ID | Status | Phase | Condition | Sponsor |
|---|---|---|---|---|
| NCT04033419 | Completed | Phase 2 | Chemo-brain / cognitive decline in breast cancer | UNC Lineberger Comprehensive Cancer Center |
| NCT01458470 | Completed | Phase 2 | Early Huntington disease (symptomatic treatment) | University of British Columbia |
| NCT00136786 | Completed | Phase 1 | Tobacco use disorder / smoking relapse prevention | New York State Psychiatric Institute |
| NCT01074619 | Completed | Phase 3 | Multiple sclerosis cognitive impairment | University Hospital, Caen |
| NCT04789915 | Recruiting | Phase 1 | Negative symptoms in first-episode psychosis | Bjorn H. Ebdrup |
| NCT04417543 | Completed | Phase 1 | Cognitive impairment in epilepsy | Assiut University |
| NCT03703856 | Completed | Phase 4 | Biomarker predictors of memantine sensitivity in AD | UC San Diego |
| NCT01658228 | Completed | Phase 4 | Memory impairment and depression combination treatment | New York State Psychiatric Institute |
| NCT01362686 | Terminated | N/A | Comparative research of Alzheimer's disease drugs | Indiana University |
| NCT02288000 | Terminated | Phase 1 | Prediction of cognitive properties for neurodegenerative diseases | University Hospital, Lille |

**Off-label and investigational use areas documented in literature:**
- Obsessive-compulsive disorder (add-on to SSRIs, positive signals) [Ref 14, Ref 24]
- PTSD (promising preclinical and early clinical data) [Ref 14]
- Schizophrenia (negative results in double-blind RCTs) [Ref 14, Ref 15]
- Bipolar disorder (add-on, antimanic effects) [Ref 14, Ref 15]
- Autism spectrum disorder in youth (recent Phase 2/3 RCT, Joshi 2025) [Ref 25]
- Opioid use disorder (adjunctive, positive with methadone/buprenorphine) [Ref 17]
- Glaucoma, HIV-associated dementia, neuropathic pain (clinical trials previously noted; results not retrieved) [Ref 7, Ref 9]
- Down syndrome (Phase 2 RCT, did not meet primary endpoint) [Ref 21]
- Vascular dementia (documented improvement in some trials) [Ref 10]

---

## Community Feedback Analysis

No community feedback was submitted in Part A2 of the brief.

---

## Gaps & Flags

### Safety-Critical Flags

1. **⚠️ EXACT TOXIC DOSE NOT ESTABLISHED:** The brief notes "exact toxic dosage is unknown" — confirmed. Only one published overdose case exists (2,000 mg), which resulted in full recovery. No LD₅₀ in humans; no dose-response toxicity data. Generation agent must preserve this uncertainty.

2. **⚠️ SIGMA-1 RECEPTOR AGONISM NOT DIRECTLY CONFIRMED:** The brief lists memantine's pharmacological class as including "Sigma-1 receptor agonist." No Ki value for memantine at sigma-1 receptors was found in primary literature. Evidence is: (a) indirect from amantadine scaffold analogy, (b) contradicted by behavioral data showing antagonistic interaction between memantine and sigma-1 agonists in AD models. The label may be incorrect or may refer to very low-affinity interaction. FLAG FOR EDITORIAL REVIEW.

3. **⚠️ RECREATIONAL DOSE SAFETY DATA ABSENT:** The database dose ranges (Threshold 10mg through Heavy 170+mg) are clinically plausible extrapolations from community reports and the drug's pharmacology, but no controlled human safety studies exist at recreational dose levels. The only acute toxicity data point is the 2,000mg overdose case. Doses above 20mg have no published controlled safety data in healthy adults.

### Data Gaps

4. **SMILES string:** Not returned by PubChem API in this run; should be fetched from CID 4054 directly.

5. **Exact Ki values at sigma-1, 5-HT₃, and nicotinic receptors:** Not found in retrieved literature. StatPearls confirms antagonism at 5-HT₃ and nicotinic receptors but does not provide Ki values. Parsons/Danysz-group primary pharmacology papers (likely from the 1990s-2000s) probably contain these values but were not retrieved.

6. **Protein binding 45% — verify basis:** Confirmed via StatPearls (FDA label-derived) but specific primary pharmacokinetic study not retrieved in this search. Acceptable for generation but note source is regulatory label.

7. **Melting point:** Physical property; not found in retrieved sources. PMC article states "white crystal or powder" but no melting point data found.

8. **History uncertainty:** "CNS activity discovered by Merz" is variously attributed to 1972 or 1982 depending on the source. Multiple sources state different years. The 1989 German launch is consistently documented. Generation agent should note this ambiguity.

9. **Effects at therapeutic doses in healthy humans:** The controlled studies in healthy participants (Noorman 2025, Noorman 2026, Lanskey 2026) used memantine primarily as a pharmacological probe for cognitive neuroscience, not to study its subjective effects. Subjective effects at therapeutic doses in healthy people are essentially undocumented in formal literature.

10. **Cross-tolerance with dissociatives:** Listed in brief without citation; pharmacodynamically plausible via NMDA receptor mechanism but specific evidence not found.

11. **Dependence formation rate:** Listed as "unknown" in brief; confirmed unknown — no published data on timeline of tolerance development.

12. **Interactions section in brief is empty:** No documented interaction severity data found. Interactions with NMDA antagonists are clinically significant and flagged in FDA labeling. Alkaline urine effect on clearance (~80% reduction) is safety-critical.