Cyclobenzaprine

Limits on what this shows

• Null findings: PubMed query "cyclobenzaprine AND (mitochondria OR mitochondrial OR ATP OR respiration)" returned three records: the Leishmania paper above, a rat respiratory-depression paper with oxycodone, and a rat liver N-oxide reduction paper; none was a mammalian mitochondrial toxicity study of cyclobenzaprine by title.

Direction

Direct mitochondrial toxicity in model systems (not a nutrient depletion).

Regulatory status

No mitochondrial warning in the cyclobenzaprine label text read [1][2].

Population evidence

Mol Cells 2015 study [6], abstract only (reconstructed by OpenAlex, not the journal page): "Both drugs triggered mitochondria-mediated neurotoxicity and oxidative stress in SH-SY5Y cells. Subchronic injections into mice produced movement deficits on the pole test" with fewer tyrosine hydroxylase-positive neurons in the substantia nigra. Concentrations, n and effect sizes were not retrieved. A cyclobenzaprine-specific paper, "Energy metabolism as a target for cyclobenzaprine: a drug candidate against visceral leishmaniasis," Bioorg Chem 2022 [14], was found by title in a PubMed listing and its abstract was opened later in this review (see the ATP production entry); it concerns a parasite and is not used to support this entry's grade.

Mechanism

Mitochondria-mediated toxicity per the abstract; steps (membrane potential, fission, Bax) were not retrievable from the abstract text and are not asserted.

Class cohort test

CLASS EXTRAPOLATION. Drugs studied: amitriptyline and desipramine. Cyclobenzaprine was not in the cohort. Capped at yellow.

Counter-evidence held on record

Counter-evidence Cell-line and rodent injection data from other drugs, at exposures not compared with cyclobenzaprine's. No human mitochondrial biomarker data for any tricyclic were retrieved. Framing caution A model-system signal from different drugs, not a confirmed clinical mitochondrial effect of cyclobenzaprine. Not a supplement indication.

Limits on what this shows

• Null findings: PubMed "cyclobenzaprine oxidative stress" returned two records: the Leishmania paper and an unrelated forced-degradation analytical chemistry paper. No human malondialdehyde, glutathione or total antioxidant capacity study was located.

Direction

Pro-oxidant in the model systems. Not depletion of a dietary antioxidant.

Regulatory status

No oxidative stress statement in the cyclobenzaprine label text read [1][2].

Population evidence

Drug-specific, Tier B: Cyclobenzaprine in L. infantum [11] (abstract via OpenAlex reconstruction): IC50 14.5 uM against promastigotes and 12.6 uM against intracellular amastigotes; oral cyclobenzaprine for five days reduced parasite burden in BALB/c mice; "CBP inhibited trypanothione reductase, increased reactive oxygen species production, and elevated IL-6 in infected macrophage co-cultures." The abstract describes trypanothione reductase as a key enzyme of trypanosome redox metabolism; whether anything comparable operates in human cells is not addressed. Class, Tier C: Mol Cells 2015 [6], "oxidative stress in SH-SY5Y cells" with amitriptyline and desipramine. The CoQ10 titles [12][13] also pair CoQ deficiency with oxidative damage or stress, by title only.

Mechanism

Parasite: inhibition of a pathogen redox enzyme plus ROS increase. Class: mitochondria-linked ROS in cells. Neither measured a systemic human marker.

Class cohort test

CLASS EXTRAPOLATION for the human-relevant part. Cyclobenzaprine was in the Leishmania study but not in any mammalian oxidative stress study. The parasite finding cannot be carried to human tissue.

Counter-evidence held on record

Counter-evidence The only cyclobenzaprine-specific data concern a parasite at micromolar concentrations in vitro and a mouse infection model. Absence of human data is not evidence of absence. Framing caution Not an antioxidant-depletion claim and not an indication for antioxidant supplements.

Limits on what this shows

• Null findings: Brain copper unchanged by either drug [9]. No human copper measurement for any tricyclic and none for cyclobenzaprine was located. The cyclobenzaprine PubMed query with copper, iron, zinc, magnesium or vitamin terms returned four records, none a copper study by title.

Direction

Depletion (serum only, rat).

Regulatory status

No copper mention in the cyclobenzaprine label text read [1][2].

Population evidence

Biol Trace Elem Res 2000 [9], abstract read: "Chronic treatment with citalopram and imipramine (but not ECS) significantly (approx 14%) decreased the serum copper level. Chronic treatment with both drugs did not alter the brain copper level." Rats; doses and durations not in the text read.

Mechanism

Absent from the abstract. No named mechanism.

Class cohort test

CLASS EXTRAPOLATION. Drugs studied: imipramine, citalopram, electroconvulsive shock. Cyclobenzaprine was not in the cohort. Because citalopram, a non-tricyclic, produced the same effect, the signal may reflect antidepressant exposure in general rather than the tricyclic structure that cyclobenzaprine shares. Capped at yellow.

Counter-evidence held on record

Counter-evidence A 14% serum change in rats with no tissue-level effect and a non-tricyclic producing the same result is a weak basis for any human claim. Framing caution Animal data from another drug. Not a deficiency claim and not a reason to supplement copper.

Limits on what this shows

• Null findings: No cyclobenzaprine iron, ferritin or hemoglobin study was located. No unexposed comparison group is described in the abstract read.

Direction

Lower serum iron in a symptomatic subgroup (association; direction of cause unknown).

Regulatory status

No iron mention in the cyclobenzaprine label text read [1][2].

Population evidence

Neuropsychobiology, "Imipramine-induced jitteriness and decreased serum iron levels" [10], abstract as reconstructed by OpenAlex: "Jitteriness appears to be a specific side effect of tricyclic antidepressant treatment in panic disorder patients. In addition, the patients with jitteriness have lower serum iron levels compared to those that do not develop jitteriness (p = 0.01)." Sample size and design details were not retrieved. OpenAlex lists 2008 for the record; the volume number suggests an earlier year and this was not resolved.

Mechanism

None established in the text read.

Class cohort test

CLASS EXTRAPOLATION. Drug studied: imipramine. Cyclobenzaprine was not in the cohort. Capped at yellow.

Counter-evidence held on record

Counter-evidence and confounding The comparison is between imipramine patients with and without jitteriness, so it cannot show that the drug lowers iron. Panic disorder is the population. Serum iron alone does not establish iron deficiency, and jitteriness is a motor side effect, not an iron status marker (Hard Rule 2). Framing caution Do not supplement iron on the basis of this entry. Excess iron has its own risks.

Limits on what this shows

• Null findings: Two of the 12 strains (F. prausnitzii, E. rectale) had MIC above 800 ug/mL for desipramine [7].

Direction

Possible composition change (antibacterial or transit-related). No nutrient direction.

Regulatory status

Generic label [1]: atropine-like action, constipation listed at 1 to 3%, dry mouth 21% (5 mg) to 32% (10 mg); no microbiome statement. Tonmya label [2]: dry mouth 3% versus 2% placebo in fibromyalgia trials; constipation not among the reported reactions in the text read. The two labels use different doses and populations.

Population evidence

In vitro only. Sci Rep 2020 [7], via a summarizing fetch of the article: six antidepressants against 12 commensal strains; "Desipramine was very active against most of the tested intestinal strains (10/12) with MIC values varying from 75 to 800 ug/mL." The fetch summary states cyclobenzaprine and other tricyclics were not tested. The authors' stated limitation is that colonic drug concentrations in humans are uncertain. No human stool study of cyclobenzaprine was located: the PubMed query "cyclobenzaprine AND (microbiome OR microbiota OR dysbiosis OR feces OR Clostridioides)" returned two records, an analytical chemistry paper and the 1978 disposition study (title only, not opened).

Mechanism

Two non-demonstrated pathways. (1) Direct antibacterial action, shown for desipramine only; the label's note of enterohepatic circulation means drug or conjugates may reach the intestine, but luminal concentration is not reported. (2) Slowed transit from anticholinergic action, which is a labeled effect; its effect on the microbiome for this drug was not studied.

Class cohort test

CLASS EXTRAPOLATION. Drug studied: desipramine (the only tricyclic in [7]). Cyclobenzaprine was not in the cohort. In vitro MICs of 75 to 800 ug/mL are far above the steady-state plasma peak in the generic label (25.9 ng/mL), so even plausibility depends on unmeasured gut exposure. Capped at yellow.

Counter-evidence held on record

Counter-evidence The concentration gap between plasma exposure and the in vitro MIC range is large. The constipation incidence in the label is low (1 to 3%). Framing caution Not a dysbiosis claim. Constipation and dry mouth are adverse effects of the drug, not nutrient deficiencies, and this entry supports no probiotic or fiber supplement recommendation.

Limits on what this shows

• Null findings: PubMed "cyclobenzaprine AND (mitochondria OR mitochondrial OR ATP OR respiration)" returned three records: this paper, a rat respiratory-depression paper with oxycodone, and a rat liver N-oxide reduction paper (titles only); neither of the latter two measured ATP. The amitriptyline and desipramine class paper [6] reports mitochondria-mediated toxicity but no cellular ATP measurement in the text retrieved. A web search for cyclobenzaprine with mitochondrial ATP or oxygen-consumption terms returned only generic assay and unrelated pages, none opened or cited. No circulating consumer claim of cyclobenzaprine "low energy" was located.

Direction

Reduced ATP and mitochondrial depolarization in the parasite model (toxic effect on the target organism, not a nutrient depletion).

Regulatory status

No ATP, energy-metabolism or mitochondrial statement in the cyclobenzaprine label text read [1][2].

Population evidence

Tier B, cyclobenzaprine in the experiment. Bioorg Chem 2022 [14], abstract only, read through a summarizing fetch of a bibliographic mirror (BVS/LILACS record of PMID 35841672); quotations are as returned by that tool and were not checked against the journal page. Quoted: "CBP caused on L. infantum promastigotes a decrease of intracellular ATP levels"; "irreversible depolarization of plasma membrane"; "collapse of the mitochondrial electrochemical potential"; "the bioenergetics metabolism as a relevant target within the lethal programme induced by CBP." The paraphrased remainder of the abstract adds mitochondrial dysfunction, reactive oxygen species, DNA fragmentation and autophagic features in the parasite. Concentrations, exposure times, n, effect sizes, any metabolomic detail and any mammalian-cell selectivity data were not in the text retrieved. Cyclobenzaprine concentrations were therefore not compared with human plasma exposure (steady-state peak 25.9 ng/mL in the generic label [1]).

Mechanism

Named in the abstract for the parasite: loss of mitochondrial membrane potential and ATP in a drug-induced lethal programme. Whether the same occurs in mammalian mitochondria at clinical exposures is not addressed in the text read. Extension to human tissue is not asserted.

Cohort test

Not a class extrapolation: cyclobenzaprine itself was tested, but in a parasite in vitro, so the evidence is Tier B and not transferable to human subjects. No human or mammalian ATP, respiration or oxidative phosphorylation study of cyclobenzaprine was located. Capped at yellow.

Counter-evidence held on record

Counter-evidence The Leishmania parasite is a different organism with a single large mitochondrion and its own redox and energy pathways; a parasiticidal effect at micromolar concentrations is the study's goal and is not an adverse effect in patients. The labeled short course (two to three weeks) and plasma levels in the ng/mL range [1] were not related to the in vitro concentrations. The fetch tool's paraphrase of the abstract mentions favorable safety considerations, but no supporting selectivity data were retrieved. Framing caution Parasite-model signal only. Not a statement that cyclobenzaprine lowers energy production in people and not a reason to take any supplement; no dose is recommended.

Limits on what this shows

• Why no grade: Dual condition met after the repair pass. The overdose case is a co-ingestion report that does not support any attribution to cyclobenzaprine, so it is not Tier B evidence for a claim, and no circulating consumer claim about cyclobenzaprine and oxygen delivery was located. Methemoglobinemia in overdose is acute toxicity, not a nutrient deficiency (Hard Rule 2). Any anemia effect through iron would be in the iron entry and is not double counted here. The FAERS result [16] is a null or counter-signal, not support for any grade, and is not reassurance either: spontaneous reports are not a measure of hemoglobin. This is a disclosed gap, not a finding of safety; re-check with a PubMed class-level query (tricyclic or muscle-relaxant exposure with hemoglobin, hematocrit or methemoglobin) and a full-text read of the FAERS preferred-term tables when access returns.

What was searched

PubMed "cyclobenzaprine AND (anemia OR hemoglobin OR hemolysis OR methemoglobin)": four records. (1) "2016 Update on Medical Overuse," not relevant. (2) and (4) two Kitamura papers on tertiary amine N-oxide reduction in rat blood and liver (drug metabolism, titles only, not opened). (3) A methemoglobinemia case in a 46-year-old man who ingested diphenhydramine, haloperidol, dolagesic, cyclobenzaprine, naproxen, cephalexin and chlorzoxazone [15] (abstract read via OpenAlex; PubMed listing year 2006, OpenAlex 2009): drug overdose with oxidizing agents, no attribution to cyclobenzaprine. Labels [1]: no mention of anemia or hemoglobin; the adverse reactions list "purpura; bone marrow depression; leukopenia; eosinophilia; thrombocytopenia" with "causal relationship unknown." Wikipedia [4]: no mention. Repair pass additions. (a) FDA FAERS pharmacovigilance analysis of cyclobenzaprine [16] (Frontiers in Medicine 2025, opened through a summarizing fetch of the article page): 2,425 cyclobenzaprine-related reports among 18,289,374 reports, Q1 2004 to Q3 2024, four disproportionality methods; "Blood and lymphatic system disorders" at system organ class level had 34 reports with ROR 0.26 (95% CI 0.18 to 0.36), meaning reported less often than background. The summary states that anemia, hemoglobin decreased, hemolysis, methemoglobinemia, hypoxia and oxygen saturation were not identified as safety signals in the text read; the full preferred-term tables were not individually reviewed. Spontaneous-report data cannot prove absence of an effect. (b) Class-level query: a Paris community cross-sectional cohort of 8,640 adults aged 50 to 75 [17] (abstract read through a summarizing fetch of a Maastricht University repository record) found lower hemoglobin with antidepressant intake overall (beta -0.100, p =.02) and with SSRIs and SNRIs (beta -0.11, p =.01) and does not report tricyclics as a signal; cyclobenzaprine is a muscle relaxant, was not an exposure, and depression itself was independently associated with lower hemoglobin. It does not support a yellow grade for cyclobenzaprine. (c) WebSearch for cyclobenzaprine with anemia, hemolytic, methemoglobinemia or hemoglobin terms returned generic methemoglobinemia case reports (titles only, none opened and none cited); a search for tricyclics with hemoglobin or red-cell terms returned titles on erythrocyte drug distribution and in vitro hemolysis, none opened.

Channel outcomes

PubMed listing: worked for this query (clean four-record result). OpenAlex single-record lookup: worked. PubMed and PMC article pages: reCAPTCHA; PubMed article page for PMID 35841672 returned 429 in the repair pass and was not retried. Crossref, Semantic Scholar, Europe PMC: rate-limited or robots-blocked. WebSearch: exhausted in the original pass, worked in the repair pass. Frontiers article page and a university repository record: opened. Mixed result: a clean small PubMed result and an opened drug-specific pharmacovigilance study that shows no signal, but class-level and consumer-claim searching remained limited by tooling.