Venlafaxine

Limits on what this shows

• Key negative/null findings: Further title-level hits from the same PubMed search were reviewed for context and not double-counted as independent confirmation of either direction: Gaur V, Kumar A, Brain Research 2010, mouse cerebral ischemia-reperfusion model, described in the search listing as showing venlafaxine protective against mitochondrial dysfunction; Kumar P, Kumar A, Behavioral Pharmacology 2010, a Huntington's-disease animal model examining venlafaxine and mitochondrial alterations, direction not confirmed from the title alone; and Głombik K et al, Cells 2021, an animal depression-plus-hypothyroidism model in which, per the PubMed listing snippet, "none of the drugs improved the decrease in the expression of mitochondrial respiratory chain enzymes," a null/negative finding for venlafaxine's ability to reverse a disease-model mitochondrial deficit, recorded here rather than omitted.
• At-risk subgroups: Cannot be determined from animal and isolated-cell data; no human mitochondrial-function study on venlafaxine was located.

Regulatory status

Not addressed in the label reviewed.

Population evidence

Scaini G et al, "Activity of mitochondrial respiratory chain is increased by chronic administration of antidepressants," Acta Neuropsychiatrica 2011. Rat, chronic dosing; title and abstract summary confirmed via PubMed search-listing and a Cambridge Core listing page, full text not opened during this review; venlafaxine's specific inclusion among the "antidepressants" tested is stated in the PubMed listing snippet but the exact dose and brain region could not be confirmed beyond the title. Ahmadian E et al, "[venlafaxine-induced mitochondrial dysfunction]," Advanced Pharmaceutical Bulletin 2016. Isolated rat hepatocytes; PubMed search-listing snippet confirms venlafaxine specifically, describing "blockade of electron transfer complexes II and IV" and reduced respiratory-chain functionality; full abstract (specific concentrations tested, and whether these were within or above therapeutic-equivalent exposure) was not accessible during this review after a DOAJ page returned a 403 error and a direct PubMed article page returned a bot-verification challenge.

Mechanism

Not unified between the two studies. The chronic in vivo finding is consistent with the broader antidepressant literature on adaptive upregulation of brain mitochondrial bioenergetics with sustained treatment; the isolated-hepatocyte finding is consistent with a direct, concentration-dependent toxicological effect on the electron transport chain outside the brain, in a system with no blood-brain-barrier-limited exposure and no adaptive/chronic dosing context.

Counter-evidence held on record

The two primary sources run in opposite directions and neither's full text was accessible during this review beyond title and search-listing snippet level; this entry should be read as "real, drug-specific, context-dependent mitochondrial effects exist" rather than as evidence that venlafaxine reliably harms or protects mitochondrial function at ordinary human dosing. Shares its respiratory-chain-complex evidence base with the ATP production entry below; see Overlap map. No mitochondrial-support supplement (CoQ10, L-carnitine, or similar) claim is supported by this entry in either direction.

Limits on what this shows

• Key negative/null findings: Xu H et al, "Dose-related effects of chronic antidepressants on neuroprotective proteins BDNF, Bcl-2 and Cu/Zn-SOD in rat hippocampus," Neuropsychopharmacology 2003 (title and PubMed search-listing snippet only, full abstract not accessible during this review), examined Cu/Zn-SOD, an antioxidant enzyme, as a dose-related outcome of chronic antidepressant treatment including venlafaxine; direction of the Cu/Zn-SOD change was not confirmed from the title alone and is carried separately into the Copper entry below rather than double-counted here.
• At-risk subgroups: Not established in humans. The Madrigal-Bujaidar 2022 finding is a single acute oral dose in mice, not a chronic-dosing human-equivalent study, and its authors' own framing of the 5 mg/kg dose as human-therapeutic-equivalent is a cross-species dose conversion, not a demonstrated human effect.

Regulatory status

Not addressed in the label reviewed.

Population evidence

Madrigal-Bujaidar E, Paniagua-Perez R, Rendon-Barron MJ, Morales-Gonzalez JA, Madrigal-Santillan EO, Alvarez-Gonzalez I, "Investigation of the DNA Damage and Oxidative Effect Induced by Venlafaxine in Mouse Brain and Liver Cells," Toxics 2022;10(12):737, DOI 10.3390/toxics10120737. Directly opened and read (mdpi.com). ICR mice (n=100 males), single oral doses of 5, 50, or 250 mg/kg (250 mg/kg representing approximately 80% of the LD50), assessed at 2, 6, 12, and 24 hours. Comet-assay DNA damage was significant in brain at 2 and 6 hours and in liver at 2, 6, and 12 hours at the 50 and 250 mg/kg doses; with the FPG enzyme (which detects oxidative DNA base damage specifically), all three doses, including the lowest (5 mg/kg, which the authors state corresponds to a high quantity of the maximum human daily therapeutic dose, approximately 375 mg/day), showed measurable oxidative DNA damage. Lipid peroxidation (malondialdehyde) rose at 6 to 12 hours with the 50 and 250 mg/kg doses; protein carbonyl content rose at 2 to 12 hours across all three doses. Abdel-Wahab BA, Salama RH, "Venlafaxine protects against stress-induced oxidative DNA damage in hippocampus during antidepressant testing in mice," Pharmacology Biochemistry and Behavior 2011;100(1):59-65. Directly opened and read (sciencedirect.com abstract). Adult male Swiss-Webster mice, venlafaxine 5, 10, or 20 mg/kg/day intraperitoneally for 21 days, forced-swim and tail-suspension stress paradigms. Venlafaxine "decreased the hippocampal MDA and NO and... increase[d] hippocampal GSH and TAC levels and GST" activity, and both serum and hippocampal 8-OHdG (an oxidative DNA damage marker) were significantly reduced versus stressed, untreated controls.

Mechanism

Not unified. The protective finding is consistent with venlafaxine's antidepressant action reducing the oxidative burden of chronic behavioral stress itself, a plausible indirect (stress-mediated) rather than direct antioxidant mechanism. The harmful finding is consistent with a direct, dose-related pro-oxidant and genotoxic effect of venlafaxine or its metabolites on brain and liver tissue, independent of any stress model, following acute single-dose oral exposure.

Counter-evidence held on record

These two studies used different species strains, different routes (intraperitoneal chronic low-dose versus oral acute dose-ranging), and different endpoints (stress-model hippocampal markers versus unstressed whole-brain/liver genotoxicity), so the "opposite direction" framing reflects genuinely different experimental contexts rather than a direct contradiction of the same measurement. Neither study supports an antioxidant-supplement recommendation around venlafaxine, and neither supports a claim that venlafaxine reliably causes oxidative harm at ordinary human dosing; this entry is retained at yellow specifically to preserve both real, drug-specific signals rather than reporting only the reassuring or only the concerning one.

Limits on what this shows

• Key negative/null findings: A dedicated PubMed search for "venlafaxine copper" surfaced no drug-specific human or animal study directly measuring copper status; the only other results were environmental/ecotoxicology papers measuring venlafaxine and copper as unrelated co-occurring water contaminants (Flynn et al 2026, Kostich et al 2017, Barbieri et al 2023), which this review did not extrapolate onto human copper physiology.
• At-risk subgroups: Cannot be determined; no dose-response or subgroup data beyond the single rat study's title-level description.

Regulatory status

Not addressed in the label reviewed; no copper-specific interaction, monitoring requirement, or warning exists in the labeling reviewed.

Population evidence

Xu H, Chen Z, He J, Haimanot S, Li X, Dyck L, Li XM, "Dose-related effects of chronic antidepressants on neuroprotective proteins BDNF, Bcl-2 and Cu/Zn-SOD in rat hippocampus," Neuropsychopharmacology 2003. Confirmed via PubMed search-listing (title, authors, journal, year); venlafaxine's inclusion among the chronic antidepressants tested is stated in the search-listing summary, but the full abstract, specific doses used for venlafaxine, and the direction (increase or decrease) of the Cu/Zn-SOD change were not accessible during this review after a direct PubMed article-page fetch returned a bot-verification challenge and an OpenAlex API lookup was rate-limited (HTTP 429) on every attempt.

Mechanism

Cu/Zn-SOD (SOD1) requires copper as an active-site cofactor; a change in the enzyme's expression or activity is a plausible, indirect marker of altered cellular copper handling or antioxidant demand, but is not itself a measurement of whole-body or serum copper status, and no source located in this review measured serum copper, ceruloplasmin, or dietary copper status in venlafaxine-treated animals or humans.

Counter-evidence held on record

This entry rests on a single source that could not be opened beyond its title and search-listing summary despite repeated attempts across three different channels (direct PubMed article page, OpenAlex API, general web search before the search budget was exhausted); the direction of the Cu/Zn-SOD change, and therefore whether this points toward increased or decreased copper-cofactor demand, is not established. Graded yellow rather than ungraded because a real, drug-specific Tier B source exists touching copper-relevant enzyme biology, but this is among the weakest-supported entries in this dossier for exactly that reason. No copper supplementation or restriction is implied. Shares its underlying source and rat-hippocampus model with the Oxidative stress entry above (Cu/Zn-SOD is itself an oxidative-stress marker); see Overlap map.

Limits on what this shows

• Key negative/null findings: A single case report, Yau AH, BMJ Case Reports 2015, titled around collagenous enterocolitis presenting with watery diarrhoea and iron-deficiency anaemia, was identified via PubMed search-listing as involving venlafaxine, but the specific causal role of venlafaxine in that patient's iron-deficiency anaemia (as opposed to venlafaxine being one of several medications listed, or the enterocolitis being the cause) could not be confirmed beyond the title during this review, so it is noted here only as unverified context, not used as supporting evidence for this entry's grade.
• At-risk subgroups: Cannot be determined; no venlafaxine-specific iron-status subgroup analysis was located.

Regulatory status

Not addressed in the label reviewed; restless legs syndrome and periodic limb movements are not listed as labeled adverse reactions in the sections reviewed.

Population evidence

Yang C, White DP, Winkelman JW, "Antidepressants and periodic leg movements of sleep," Biological Psychiatry 2005. Human, n=274 patients undergoing polysomnography; confirmed via PubMed search-listing (title, authors, journal, year, sample size), full text not accessible during this review after a publisher-site fetch returned a 403 error. Kouri I et al, "Restless Legs Syndrome and Periodic Limb Movements of Sleep: From Neurophysiology to Clinical Practice," Journal of Clinical Neurophysiology 2023, a review confirmed via PubMed search-listing as noting "higher rates for mirtazapine and venlafaxine" for restless-legs-type symptoms among antidepressants, title/listing level only. Neither source directly measured iron, ferritin, or transferrin saturation in venlafaxine users; the iron connection instead rests on the general restless legs syndrome literature (not venlafaxine-specific), which broadly implicates reduced CNS iron availability (evidenced in that separate literature by brain-iron imaging and cerebrospinal-fluid ferritin studies not reviewed here as they are unrelated to venlafaxine) in RLS pathophysiology.

Mechanism

Not established for venlafaxine directly. The inference chain is: (1) venlafaxine is associated with increased periodic limb movements/restless-legs-type symptoms in human comparative sleep-study data, a real, drug-specific finding; (2) restless legs syndrome in general (regardless of cause) is mechanistically associated with CNS iron insufficiency in the broader RLS literature; therefore (3) it is mechanistically plausible, but not demonstrated, that venlafaxine-associated RLS symptoms could relate to CNS iron handling. Step 3 was not directly tested by any source located in this review.

Counter-evidence held on record

This is the entry in this dossier furthest removed from a direct measurement: no source located measured iron status in venlafaxine users at any tier, and the RLS-iron mechanistic link itself comes from the general RLS literature, not from venlafaxine-specific research. This entry must never be read as "venlafaxine causes iron deficiency"; it states only that venlafaxine is associated with a symptom (periodic limb movements/restless-legs-type symptoms) whose general pathophysiology elsewhere in the literature implicates iron. No iron supplementation is recommended from this entry; a patient developing new restless-legs symptoms on venlafaxine warrants clinical evaluation (which may include ferritin testing per standard RLS workup) rather than self-directed iron supplementation, since iron supplementation without documented deficiency carries its own risk (see Monitoring panel and Scope and limits).

Limits on what this shows

• Key negative/null findings: No human gut-microbiome study of venlafaxine was located in this review. No study located quantified whether venlafaxine's microbiome effects are clinically meaningful (for example, via reduced short-chain-fatty-acid production or secondary nutrient-synthesis effects) as opposed to a measurable but functionally unclear compositional shift.
• At-risk subgroups: Cannot be determined from animal and in vitro data alone.

Regulatory status

Not addressed in the label reviewed.

Population evidence

Ait Chait Y et al, in vitro study (title and Europe PMC search-listing snippet confirm "antimicrobial action" against gut bacteria for a panel of antidepressants including venlafaxine, 2020); full text and exact journal citation were not independently reconfirmed during this review after a direct attempt to open it returned an unrelated paper, so this citation is used at the title/listing-confirmed level only. Shen et al, Behavioural Brain Research 2023, mice, chronic-stress depression model, venlafaxine altered gut bacterial composition (title/listing level). Chen et al, Metabolic Brain Disease 2024, mice, venlafaxine treatment produced measurable changes in microbiota and metabolite profiles associated with treatment response (title/listing level). Du et al, Frontiers in Psychiatry 2024, cuprizone-demyelination mouse model, venlafaxine improved depressive-like behavior alongside altered microbiota (title/listing level). Serrano-Contreras JI et al, Journal of Pharmaceutical and Biomedical Analysis 2016, rats, metabolic response to venlafaxine examined within the gut-microbiome-brain axis (title/listing level). Cussotto S et al, Psychopharmacology 2019, and Lukic I et al, Translational Psychiatry 2019, both animal studies of psychotropic/antidepressant effects on microbiome composition, reviewed at title/listing level and not confirmed as venlafaxine-specific beyond the search-listing description.

Mechanism

Direct antimicrobial activity against gut bacterial species in vitro is the most drug-specific and least confounded mechanism located; the animal composition-change studies are consistent with this but cannot separate a direct antimicrobial effect from an indirect effect mediated by altered gut motility, appetite, or host behavior/diet under chronic venlafaxine treatment.

Counter-evidence held on record

Most of this entry's supporting citations were confirmed only at the title and PubMed/Europe PMC search-listing level, not from an opened abstract or full text, a limitation stated explicitly here and in the Sources list; the in vitro antimicrobial finding is the strongest single piece of evidence but was also not independently reopened and reconfirmed beyond its search-listing description during this review. No probiotic or microbiome-support supplement recommendation follows from this entry. It is retained at yellow, not ungraded, because multiple independent animal and in vitro sources, not merely a single hit, converge on a real drug-specific microbiome signal even though none was opened to full-text depth.

Limits on what this shows

• Key negative/null findings: Targeted PubMed searches combining venlafaxine with hemoglobin, hematocrit, or anemia (multiple phrasings) returned no dedicated venlafaxine-specific hematology outcome study, only the labeled adverse-reaction categories above and off-target results; this review found no evidence that venlafaxine lowers hemoglobin or hematocrit at ordinary therapeutic doses outside this uncommon/rare labeled-event pattern, and no evidence of a dose-response relationship.
• At-risk subgroups: Not defined beyond the label's general bleeding-risk cautions (concurrent aspirin, NSAIDs, warfarin, or other antiplatelet/anticoagulant therapy; a bleeding diathesis).

Regulatory status

Labeled adverse-reaction data (Tier A, drug-specific), reviewed via drugs.com's side-effects compilation of the FDA-approved labeling and independently cross-checked against DailyMed's own Section 6.2: clinical-trial frequency category "Uncommon (0.1% to 1%): Anemia, leukocytosis, leukopenia, lymphadenopathy, mucous membrane bleeding, mucosal hemorrhage, thrombocythemia, thrombocytopenia"; "Rare (less than 0.1%): Agranulocytosis, aplastic anemia, basophilia, blood dyscrasias, eosinophilia, lymphocytosis, neutropenia, pancytopenia, prolonged bleeding time." DailyMed's Section 6.2 Postmarketing Experience, Hemic/Lymphatic System, independently confirms: "blood dyscrasias (including agranulocytosis, aplastic anemia, neutropenia and pancytopenia)," "thrombocytopenia," "prolonged bleeding time," "mucous membrane bleeding."

Population evidence

These are labeled frequency categories drawn from venlafaxine's own clinical trial and postmarketing surveillance datasets (Tier A, drug in the cohort by definition), not a dedicated hematology outcome study; no denominator, confidence interval, or comparison-arm incidence beyond the categorical frequency band is available from the label text itself.

Mechanism

Not established as a direct nutrient- or iron-status mechanism. Two plausible, non-exclusive pathways are named in the label's own broader safety data rather than proven causal for the anemia signal specifically: (1) serotonin-transporter-mediated platelet dysfunction, the same mechanism behind venlafaxine's labeled increased bleeding risk (Section 5.4: drugs that interfere with serotonin reuptake "may increase the risk of bleeding events, ranging from ecchymoses, hematomas, epistaxis, petechiae, and gastrointestinal hemorrhage to life-threatening hemorrhage"), which could plausibly contribute to anemia through chronic occult blood loss in a minority of patients; and (2) idiosyncratic, immune-mediated bone-marrow suppression, the pattern implied by the rare agranulocytosis/aplastic-anemia/pancytopenia postmarketing cluster, a mechanism shared with other serotonergic and non-serotonergic psychotropics and not specific to venlafaxine's own pharmacology.

Counter-evidence held on record

This entry is bounded specifically to the label's own "uncommon" and "rare" frequency categories; it is not a claim that venlafaxine commonly or predictably lowers oxygen-carrying capacity, and no controlled study quantifying an average hemoglobin or hematocrit change on venlafaxine was located. Venlafaxine's dose-related blood-pressure increase (see Pharmacokinetic basis) is a separate, non-hematologic pharmacodynamic effect and is not part of this entry; per Hard Rule 2 it is not graded as an oxygen-delivery deficiency. No iron or other supplementation is implied by this entry; unexplained fatigue, pallor, or bleeding on venlafaxine warrants a complete blood count under medical supervision, not self-directed supplementation.

Limits on what this shows

• Key negative/null findings: No study located in this review directly measured ATP yield, cellular respiration rate, or energy charge after venlafaxine administration, in animals or humans; this entry is one inferential step removed from a direct ATP measurement, the same limitation noted in the Mitochondrial burden entry's respiratory-chain-complex data, which this entry partly shares (see Overlap map).
• At-risk subgroups: Cannot be determined from a single rat chronic-stress model; no human data located.

Regulatory status

Not addressed in the label reviewed.

Population evidence

Brivio P, Audano M, Gallo MT, et al, "Venlafaxine's effect on resilience to stress is associated with a shift in the balance between glucose and fatty acid utilization," Neuropsychopharmacology 2023;48(10):1475-1483. Directly opened and read (nature.com). Rats, chronic mild stress (CMS) paradigm, ventral hippocampus, metabolomic profiling of energy-metabolite concentrations. "A shift from glycolysis to beta oxidation seems to be responsible for the vulnerability to chronic stress," and venlafaxine treatment was associated with normalizing this toward glucose-based metabolism; the study is framed around metabolic substrate rebalancing rather than a direct measurement of ATP yield or mitochondrial respiration rate.

Mechanism

Substrate-switching between glycolysis and beta-oxidation as a determinant of cellular energy availability under chronic stress; venlafaxine's association with reversing a stress-linked shift toward fatty-acid oxidation implies an effect on energy-substrate selection, though the causal direction (whether venlafaxine acts directly on substrate-selection machinery or indirectly via its antidepressant/anti-stress effect) is not established by this single study.

Counter-evidence held on record

This entry rests on a single, indirect metabolomic endpoint (substrate balance, not ATP yield) and shares its underlying respiratory-chain-complex evidence with the Mitochondrial burden entry above. No energy-support supplement recommendation (CoQ10, creatine, B-vitamins for energy metabolism, or similar) follows from this entry. See Overlap map for the shared evidence basis with Mitochondrial burden.