Skip to content
StackItSmart
BHuman cohort / observational

NAC

N-Acetyl Cysteine

N-Acetylcysteine (NAC) is the acetylated form of the amino acid L-cysteine and a precursor to glutathione, the body's principal intracellular antioxidant. Its best-established medical use is as the antidote for acetaminophen (paracetamol) overdose, where it replenishes hepatic glutathione and prevents liver failure; it is also used clinically as a mucolytic in chronic bronchitis/COPD. In the supplement/"organ-support" context it is taken orally as an antioxidant and putative liver-support agent, but direct human evidence that it protects the liver or kidneys during anabolic-steroid or other drug use is essentially absent — that use is extrapolated, not proven. The main risks are that intravenous NAC causes dose-related anaphylactoid (non-allergic) reactions in a meaningful minority of patients — flushing, hives, bronchospasm, hypotension, and rarely chest pain with ECG changes — and that gastrointestinal upset (nausea, vomiting, diarrhea) can occur with oral dosing and is a reason to reduce or stop. Oral NAC has very low and variable bioavailability. NAC is not a substitute for medical care: anyone who has taken a paracetamol overdose or has signs of liver injury needs emergency evaluation and clinician-directed dosing, not self-treatment.

Clinical readoutAncillary · organ-support
Hepatic strainNone
CardiovascularModerate
HPTA suppressionNone
Half-life
Reduced NAC termi…
Route
Oral
Evidence
B
Active
Short
1·t½2·t½3·t½4·t½5·t½
Illustrative single-compartment washout · each mark = one half-life · t½ ≈ Reduced NAC terminal half-life ~1.95 h after IV dosing; total NAC (including protein-bound/oxidized forms) ~5.6 h IV and ~6.3 h oral, in healthy volunteers (Olsson 1988).
Pharmacology

Mechanism of action

NAC is deacetylated to L-cysteine, the rate-limiting substrate for synthesis of glutathione (GSH). By restoring/augmenting intracellular GSH it neutralizes reactive oxygen species and detoxifies the reactive acetaminophen metabolite NAPQI, which is the basis of its antidotal effect in paracetamol poisoning (NAPQI depletes GSH, then covalently binds mitochondrial proteins, triggering oxidant stress, peroxynitrite formation and hepatocyte necrosis). NAC's free sulfhydryl (thiol) group also directly scavenges free radicals and cleaves disulfide bonds in mucus glycoproteins, reducing sputum viscosity (mucolytic action). In the CNS, NAC is proposed to modulate the cystine-glutamate antiporter and glutamatergic neurotransmission, the rationale for its investigational psychiatric use.
Kinetics

Pharmacokinetics

Half-life

Reduced NAC terminal half-life ~1.95 h after IV dosing; total NAC (including protein-bound/oxidized forms) ~5.6 h IV and ~6.3 h oral, in healthy volunteers (Olsson 1988).

Active duration

Short; typically dosed multiple times daily. Clinical antidote and mucolytic regimens rely on repeated/continuous administration rather than a single long-acting dose.

Route

Oral (capsule/effervescent tablet) for supplement/mucolytic use; intravenous and oral formulations used clinically as the paracetamol antidote; inhaled/nebulized as a mucolytic.

Metabolism & clearance

Low oral bioavailability (~4% for reduced NAC, ~6–10% for total NAC) due to extensive gut and first-pass metabolism; volume of distribution ~0.5 L/kg. Deacetylated to cysteine and incorporated into glutathione and other endogenous thiols; metabolites and conjugates undergo predominantly renal clearance. Half-life is prolonged in hepatic impairment.

For monitoring and washout planning, not drug-test evasion.

Reported effects

Physiological & performance effects

  • Replenishes hepatic glutathione and serves as the standard antidote for acetaminophen/paracetamol overdose, reducing hepatotoxicity and death when given early
  • Mucolytic: reduces sputum viscosity; oral mucolytics (including NAC) modestly reduce exacerbations in chronic bronchitis/COPD (Cochrane meta-analysis)
  • Antioxidant / free-radical scavenger via thiol group and glutathione precursor role
  • Investigational adjunct in several psychiatric conditions (e.g., autism spectrum irritability/hyperactivity, OCD) with mixed and unestablished efficacy
  • Used as adjunctive therapy in amatoxin (mushroom) poisoning, though benefit is unproven
  • No demonstrated performance-, muscle-, or body-composition-enhancing effect
Safety

Adverse effects by system

Cardiovascular

Intravenous NAC can cause anaphylactoid reactions including hypotension, tachycardia, flushing and, rarely, chest pain with ECG changes (ST-segment depression, T-wave inversion). These are non-allergic, dose/rate-related histamine-mediated reactions, not evidence of intrinsic cardiotoxicity. No established adverse cardiovascular effect from standard oral use.

Hepatic

NAC is hepatoprotective, not hepatotoxic; it is the antidote for paracetamol-induced liver injury. No credible signal of liver injury from NAC itself.

Endocrine / HPTA

NAC is not a hormonal agent and has no established effect on the male hypothalamic–pituitary–testicular axis, testosterone, LH or FSH. In women with PCOS it has been studied for ovulation/insulin endpoints, but this does not indicate androgen-axis activity in men. No adequate human data suggest HPTA suppression.

Reproductive

No adverse reproductive effect established. Antioxidant supplements including NAC have been studied for male-factor infertility/semen parameters, with variable results and a need for confirmatory RCTs; this is a putative benefit, not an adverse effect.

Neuropsychiatric

No established adverse psychiatric effects; NAC is generally reported as safe and tolerable in psychiatric trials. Efficacy for psychiatric indications (OCD, autism) remains unproven, not harmful per se.

Renal

No nephrotoxicity attributed to NAC. Despite widespread historical use to prevent contrast-associated acute kidney injury, the large PRESERVE RCT found oral NAC provided no renal protection. Renal clearance predominates, so dosing caution is warranted in renal impairment.

Hematologic

No clinically significant hematologic toxicity established. NAC's thiol/antiplatelet and nitric-oxide-related effects are described mechanistically but no consistent bleeding or cytopenia signal exists in humans at usual doses.

Dermatologic

Cutaneous anaphylactoid reactions (flushing, urticaria/hives, rash, angioedema) are the most common adverse reactions to intravenous NAC; they are usually manageable with antihistamines and are less frequent with oral dosing.

Recovery

HPTA suppression & recovery

Suppression: None expected — NAC is not a steroid, SERM, or hormonal modulator and has no established suppressive effect on the male HPTA axis.

Because NAC does not suppress the hypothalamic–pituitary–testicular axis, no post-use HPTA recovery protocol is applicable to NAC itself. Any concerns about testosterone, LH/FSH, or recovery after suppressive compounds should be evaluated with bloodwork and managed by an endocrinologist; NAC is not a treatment for HPTA suppression.

Bloodwork & vitals

Monitoring

Recommended labs & checks
Liver function tests (ALT, AST, bilirubin, INR) if used in the context of paracetamol exposure or suspected liver injurySerum acetaminophen concentration and standard toxicology work-up in overdose settings (clinician-directed)Renal function (creatinine/eGFR) at baseline in those with kidney impairmentBaseline clinical review before any intravenous administration

Cadence: For routine oral supplement use, no specific mandated lab schedule exists; obtain baseline labs and periodic bloodwork if using chronically or alongside hepatotoxic/nephrotoxic agents. In overdose/clinical use, monitoring is intensive and clinician-directed per protocol.

Warning signs — seek care
  • Signs of anaphylactoid reaction: widespread flushing, hives, facial/throat swelling, wheeze or shortness of breath, lightheadedness — stop and seek care
  • Chest pain, palpitations, or fainting during infusion
  • Persistent vomiting or inability to tolerate oral dosing
  • Right-upper-quadrant pain, jaundice, dark urine, or confusion (possible liver injury requiring emergency care)
  • Any suspected paracetamol overdose — go to emergency services immediately
Do not use if

Contraindications

  • Known hypersensitivity to acetylcysteine
  • Active bronchospasm / poorly controlled asthma — caution, as NAC (especially inhaled/IV) can provoke bronchospasm
  • Prior severe anaphylactoid reaction to intravenous NAC
  • Active peptic ulcer or significant GI intolerance — oral dosing can worsen gastrointestinal symptoms
  • Use of intravenous NAC should be clinician-supervised due to anaphylactoid reaction risk
  • Self-treatment of suspected acetaminophen overdose instead of emergency care is dangerous — seek emergency evaluation
Combinations

Interaction profile

  • ContraindicatedWith DNP: Additive cardiovascular strain

Check a specific combination in the interaction checker.

Harm reduction

Reducing harm & when to stop

  • NAC is not a substitute for medical care: suspected acetaminophen overdose or any sign of liver injury (RUQ pain, jaundice, dark urine, confusion) is a medical emergency — call emergency services; antidotal dosing must be clinician-directed.
  • Do not self-administer intravenous NAC; IV use carries anaphylactoid reaction risk and requires medical supervision.
  • If taking oral NAC and you develop widespread flushing, hives, facial/throat swelling, or wheezing, stop and seek care — these can signal an anaphylactoid/allergic reaction.
  • People with asthma should be cautious, as NAC can provoke bronchospasm.
  • Do not rely on NAC as proven 'liver' or 'kidney protection' during anabolic-steroid or other drug use — there is no adequate human evidence it prevents drug-induced organ injury in that setting; the large PRESERVE trial found no kidney benefit.
  • If gastrointestinal upset (nausea, vomiting, diarrhea) occurs with oral dosing, reduce the dose or stop if symptoms are severe or persistent.
  • Get baseline and periodic bloodwork (liver and kidney function) and involve a clinician if using chronically or alongside hepatotoxic/nephrotoxic substances.
  • Discuss any hormonal or recovery concerns with an endocrinologist — NAC does not treat HPTA suppression.
Evidence

Citations (12)

Every clinical claim above is tied to a primary source. Overall evidence grade B — graded to the best available evidence for its core claims.

  1. 01

    NAC is the effective antidote for acetaminophen/paracetamol overdose and prevents hepatotoxicity by restoring glutathione.

    ReviewPMID 37436926 ↗

  2. 02

    Mechanism: acetaminophen overdose depletes glutathione and forms reactive NAPQI causing mitochondrial oxidant stress and hepatocyte necrosis; NAC (glutathione precursor) is an effective antidote.

    ReviewPMID 38265880 ↗

  3. 03

    Human oral bioavailability of NAC is very low (~4% reduced, ~6–10% total) with IV terminal half-life ~1.95 h (reduced) / ~5.6 h (total) and Vd ~0.5 L/kg.

    RCTPMID 3360052 ↗

  4. 04

    Intravenous NAC causes dose-related anaphylactoid (non-allergic) reactions — cutaneous and systemic — manageable with antihistamines.

    Case seriesPMID 9624310 ↗

  5. 05

    Anaphylactoid reactions to IV NAC can include chest pain, tachycardia and ECG changes (ST depression, T-wave inversion); reported in up to ~3% of patients.

    Case reportPMID 1606339 ↗

  6. 06

    Cutaneous anaphylactoid reactions and medication errors occur with IV NAC regimens (pediatric cohort comparing two-bag vs three-bag).

    CohortPMID 35587124 ↗

  7. 07

    Oral NAC provided no benefit over placebo for preventing acute kidney injury, dialysis or death after angiography (PRESERVE RCT).

    RCTPMID 29130810 ↗

  8. 08

    Oral mucolytics including NAC modestly reduce exacerbations in chronic bronchitis/COPD without an increase in adverse events.

    Meta-analysisPMID 31107966 ↗

  9. 09

    NAC in autism spectrum disorder is safe and tolerable and may reduce hyperactivity/irritability, but further evidence is needed before recommendation.

    Meta-analysisPMID 32900213 ↗

  10. 10

    NAC is among agents with preliminary but not established efficacy as an adjunct in obsessive-compulsive disorder.

    ReviewPMID 28384832 ↗

  11. 11

    NAC is used adjunctively in amatoxin (mushroom) poisoning with anaphylactoid reactions ~5%, but benefit remains unproven.

    ReviewPMID 32609548 ↗

  12. 12

    Antioxidant supplements including NAC have been studied for male-factor infertility/semen parameters with variable results requiring confirmatory RCTs.

    ReviewPMID 23775385 ↗

Last reviewed 2026-07-06 · Verified against PubMed · Educational, not medical advice