Acetylcysteine

Limits on what this shows

• Null findings: A human study of muscle mitochondrial respiration after sprint training with acute NAC infusion reported the training effect on respiration; an NAC effect on respiration was not given in the page read [29]. Mitochondrial DNA copy number was no different with NAC in an IVF trial of 200 women (P=0.157; DOAJ listing summary) [28].

Regulatory status

No mitochondrial statement in the labels read [1][2][3].

Population evidence

Tier B in vitro (L6 rat myoblasts): 1 mM NAC decreased maximal mitochondrial respiration and increased H2O2 production; a one-week pretreatment produced adaptation, more mitochondrial content and lower cellular ROS [26]. Tier B rats, high-fat diet plus NAC 500 mg/kg/day for 8 weeks: salivary gland complex I activity +42% (parotid) and +68% (submandibular) versus high-fat diet alone, cytochrome c oxidase -40% and -23% [27]. Tier C (glycine co-administered, no NAC-alone arm), per DOAJ listing abstracts only: 14 days of glycine plus NAC in 10 adults with type 2 diabetes raised fasted mitochondrial fatty-acid oxidation 30%; an open-label 12-week study in 8 people with HIV reported improved mitochondrial and other defects [28].

Mechanism

Reductive stress is named in [26]; the human combination studies cannot attribute effects to NAC.

Counter-evidence held on record

Counter-evidence Direction is inconsistent across models; the in vitro concentration is far above plasma levels after oral doses (peak 26.5 mcg/mL after 11 g, per the label summary [3]). Cohort test: no human study with NAC alone. Framing caution Theoretical. Not a mitochondrial toxicity claim and not a mitochondrial benefit claim.

Limits on what this shows

• Null findings: Glycine plus NAC for 14 days in 117 older adults (no NAC-alone arm) did not change whole-blood total glutathione, the GSH:GSSG ratio or MDA versus placebo [20]. In 77 endurance-trained adults, 1,200 mg/day for 7 days did not change reduced glutathione overall [19].
• At-risk subgroups: Benefit signals come from disease populations (sickle cell disease, thalassemia, hemodialysis, exercise stress). Not defined for healthy people.

Regulatory status

The inhalation/oral label states acetylcysteine likely restores glutathione or acts as an alternate substrate for detoxifying the reactive acetaminophen metabolite [2]. No oxidative-stress warning.

Population evidence

Meta-analysis of 28 controlled clinical trials (abstract only read; participant numbers, doses and GSH, TAC, SOD, GPx results not retrieved): malondialdehyde SMD -1.44 (95% CI -2.05 to -0.84, P<0.001); IL-8 WMD -2.56 pg/mL (-3.89 to -1.23); CRP SMD -0.1 (-0.52 to 0.32), no effect [14]. Crossover study, 8 untrained men, IV NAC versus saline: exercise-induced fall in reduced glutathione and rise in oxidized glutathione were attenuated [23]. RCT in 44 children with beta-thalassemia major, NAC 10 mg/kg for 3 months: total oxidant status 8.88 to 6.84 versus 7.93 to 8.66 in controls, between-group P=0.014 [11].

Mechanism

Named: cysteine donation for glutathione synthesis and direct thiol redox activity [2]. Opposite signal at high concentration in vitro: rat L6 myoblasts exposed to 1 mM NAC showed reduced maximal mitochondrial respiration and increased H2O2 production, followed by adaptation after one week [26].

Counter-evidence held on record

Counter-evidence and confounding The meta-analysis pools heterogeneous diseases and was read at abstract level only. The one direct null in healthy older adults used a glycine combination. Antioxidant effects in disease are not a finding about healthy-person oxidative status. Framing caution Not an antioxidant benefit claim and not a deficiency claim. Acetylcysteine should not be described as depleting antioxidants, nor as a proven antioxidant for healthy people.

Limits on what this shows

• Null findings: Healthy endurance-trained adults, 1,200 mg/day for 7 days (n=77): reduced glutathione unchanged overall [19]. In the IV exercise study, whole-blood total glutathione was not changed by NAC [24]. Glycine plus NAC in older adults: no change in whole-blood glutathione [20].
• At-risk subgroups: Not a risk entry. Lower baseline glutathione (sickle cell disease) is where change was seen.

Regulatory status

Mechanism stated in the label: restores glutathione or serves as an alternate substrate for conjugation [2]; cysteine and glutathione named as metabolites [1].

Population evidence

Pace 2003, phase II double-blind randomized trial, 21 subjects with sickle cell disease: at 2,400 mg/day red-cell glutathione rose from 292.8 +/- 74.5 to 576.7 +/- 155.1 (P<0.05; units not stated in the abstract read), and dense cells fell from 20.1 +/- 2.9% to 12.6 +/- 2.1% [21]. Nur 2012, open-label randomized pilot, 11 patients on 1,200 or 2,400 mg/day for 6 weeks: whole-blood glutathione increased (values not in the abstract read) [22]. Medved 2004, crossover, 8 men, IV NAC: muscle cysteine and cystine rose above pre-infusion levels with NAC (P<0.001) [24].

Mechanism

Named and label-supported [2]. Two independent Tier A trials with glutathione directly measured and a consistent direction exist, but the finding is a repletion (reverse direction), so Step 7 holds it at yellow.

Counter-evidence held on record

Counter-evidence and confounding Small trials, disease-specific, one open-label. Units for the 2003 glutathione values were not stated in the abstract. Cohort test: acetylcysteine was the studied drug in [21][22][24]; [20] is a combination and is used only as a null. Framing caution Not a deficiency claim and not a supplement recommendation. Glutathione repletion in a disease subgroup says nothing about healthy status.

Limits on what this shows

• Null findings: The human oral study above. The same mouse study measured no serum copper [7].
• At-risk subgroups: None defined. High-dose IV exposure is the only theoretical group, untested for copper.

Regulatory status

No copper statement in the labels read [1][2][3]. The inhalation label's copper reference concerns equipment reactivity only [2].

Population evidence

Hjortsø 1990 (Eur J Clin Pharmacol 39:29-31), self-controlled study, 10 healthy volunteers (7 women, 3 men, mean age 41), NAC 200 mg three times daily for 2 weeks: plasma copper 15.1 to 15.9 umol/L across periods and urinary copper/creatinine stable; "No statistically significant change in the concentration or urinary excretion of calcium, magnesium, iron, zinc or copper" [6]. Read from a third-party copy of the paper. Mouse study (Tier B), male C57BL/6 mice, 1 g NAC per 100 mL drinking water for 20 weeks: copper decreased in liver and spleen and was unchanged in duodenum; the authors call the effects "rather small"; serum copper and ceruloplasmin were not measured [7]. In cadmium-exposed rats, NAC 50 mg/kg raised serum and liver copper relative to cadmium alone (injury-model context, not an NAC-alone effect) [8].

Mechanism

Thiol-metal binding is plausible; its physiological relevance is limited by oral bioavailability of 6 to 10% [5]. The Hjortsø paper states chelation was reported earlier only with high IV doses and cites a 1973 study of heavy-metal complexing with 3 g IV (secondhand, not opened) [6].

Counter-evidence held on record

Counter-evidence n=10, 2 weeks, oral only, no ceruloplasmin. The mouse dose is far above human use. No human copper measurement during IV therapy was found. Framing caution Mechanistic signal only; not a deficiency claim and not a reason to supplement copper.

Limits on what this shows

• Null findings: Plasma iron (healthy volunteers) and ferritin (thalassemia) unchanged [6][11].
• At-risk subgroups: None defined. Co-ingestion of large iron doses is the rat model's context and not a finding in people.

Regulatory status

No iron statement about body iron in the labels read [1][2][3]; the inhalation label's iron reference is equipment handling [2].

Population evidence

Hjortsø 1990: plasma iron 15.1 to 21.3 umol/L across periods, no significant change (n=10) [6]. RCT in 44 children with beta-thalassemia major, NAC 10 mg/kg for 3 months: ferritin 3464.5 to 3293 versus 1603.77 to 1886.33 in controls, no within-group change (P=0.889 and 0.465); the paper's two tables give different baseline ferritin for the NAC group [11]. Hemodialysis RCT, 51 patients, 1,200 mg/day for 1 month: ferritin fell within the NAC group (P=0.006) with higher baseline ferritin in that group (P=0.02), alongside a fall in hs-CRP (P=0.02) [12]. Through a DOAJ listing summary only: a 40-patient hemodialysis RCT with no significant between-group ferritin difference, and a single-arm 24-patient study with ferritin 632.0 to 515.1 [13]. Rat acute iron intoxication (400 mg/kg iron by gavage): adding oral NAC raised serum iron and mortality (P<.001); the authors suggest increased GI iron absorption [9]. In rats given 100 mg/kg iron intraperitoneally for weeks, NAC lowered serum iron, ferritin and TIBC (one article's unit labels look unusual) [10].

Mechanism

Proposed only in animals: thiol reduction of ferric iron could raise absorption in an overdose; opposite effects in chronic parenteral loading.

Counter-evidence held on record

Counter-evidence and confounding Ferritin is an acute-phase reactant, and hemodialysis ferritin changes track inflammation, so they are not an iron-depletion finding (Hard Rule 3). Anemia is an outcome, not iron deficiency (Hard Rule 2). Framing caution Not a deficiency claim. The rat excess-direction finding is not a human recommendation; no iron supplement is recommended or discouraged here.

Limits on what this shows

• Null findings: No diversity change in the rat perfusion [30]. DOAJ search for acetylcysteine AND microbiota (25 records) found no human oral-systemic NAC gut composition trial.

Direction

Mostly nutrient-or-microbe acting on the drug (Hard Rule 4), not the drug depleting anything.

Regulatory status

No microbiome statement in the labels read [1][2][3].

Population evidence

Tier B, Nature Communications 2025: in germ-free versus specific-pathogen-free rats, NAC effective permeability was about twice as high in germ-free rats (1.446 x 10^-4 cm/s plateau); NAC perfusion in SPF rats enriched Bacteroides thetaiotaomicron and B. fragilis with no difference in alpha or beta diversity; bacterial serine palmitoyltransferase converts NAC-derived cysteine into cysteine-3-ketosphinganine, lowering permeability. Intestinal fluid from 319 healthy adults trained a permeability prediction model; effects of NAC dosing on human gut composition were not reported in the summary read [30]. Tier A but non-gut: in a randomized trial of experimental gingivitis (30-person prevention and 20-person treatment sub-studies), NAC mouthwash had a modest effect on the subgingival microbiome by 16S sequencing [31].

Mechanism

Named for the microbe-to-drug direction [30]; not shown for a harmful change in microbiome by NAC.

Counter-evidence held on record

Counter-evidence Rat-based, acute perfusion; the mouthwash result is a different route and body site. PubMed searches for this category were rate-limited. Framing caution Not a dysbiosis claim. Do not infer gut microbiome harm from oral or IV use.

Limits on what this shows

• Null findings: [23] found no change in time to fatigue.

Regulatory status

No energy-metabolism statement in the labels read [1][2][3].

Population evidence

Tier B: high-fat-diet rats given NAC 500 mg/kg/day for 8 weeks had ADP/ATP ratio about 20% lower (parotid) and 24% lower (submandibular) than high-fat-diet controls [27]. In vitro 1 mM NAC reduced maximal respiration in myoblasts; ATP was not reported in the page read [26]. Human functional outcomes (not ATP): IV NAC extended time to fatigue at 92% VO2peak by 26.3 +/- 9.1% (6.4 +/- 0.6 versus 5.3 +/- 0.7 min, P<0.05; 8 men) [24], but in another crossover of 8 men time to fatigue did not differ (about 102 versus 107 s) [23].

Mechanism

Not demonstrated. Exercise outcomes are not ATP production and are not used as such.

Counter-evidence held on record

Counter-evidence Single animal model with a disease-induced baseline. Kept independent of Mitochondrial burden and Oxygen delivery/utilization (Hard Rule 7); shared sources are in the Overlap map. Framing caution Not a "low energy" claim and not an energy-boosting claim.

Limits on what this shows

• Null findings: Hemodialysis RCT: no benefit on anemia [12]. Hemoglobin was not the primary outcome in several of these studies.

Regulatory status

No hemoglobin or methemoglobin warning in the three labels read; hypersensitivity and bronchospasm are the label warnings [1][2][3].

Population evidence

Thalassemia major RCT, 44 children, 10 mg/kg for 3 months: hemoglobin at month 3 6.79 +/- 1.05 versus 5.84 +/- 0.88 g/dL (P=0.002) [11]. Hemodialysis RCT, 51 patients, 1,200 mg/day for 1 month: hematocrit fell within the NAC group (P=0.002) and "NAC was not effective in treatment of anemia" [12]. Through DOAJ listing summaries only: uncontrolled hemodialysis studies (42 children, 3 months; 26 adults, 600 mg twice daily, 2 months, P=0.005) reported hemoglobin increases [13]. Sickle cell disease pilot, 11 patients: cell-free hemoglobin decreased [22]; a 2024 Cochrane review of antioxidants for sickle cell disease (26 studies, 1,609 participants) found no clear benefit of NAC 1,200 mg over placebo for crises, pain or quality of life [37].

Mechanism

Absent for impaired oxygen delivery. A hemolysis, thrombocytopenia and renal failure case after an iatrogenic NAC overdose was seen only as a listing snippet (not opened). No G6PD-specific NAC hemolysis study was found; NAC was a co-treatment in a naphthalene poisoning case with methemoglobinemia, where its effect cannot be separated.

Counter-evidence held on record

Counter-evidence and confounding Findings are inconsistent across populations and mostly small or uncontrolled. Anemia and hemoglobin are outcomes, not nutrient measures (Hard Rule 2). Any iron-related reading is handled in the Iron entry. Framing caution Not an oxygen-delivery deficiency claim in either direction.