Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
TYLENOL W/ CODEINE NO. 4 vs ACETAMINOPHEN, ASPIRIN, AND CODEINE PHOSPHATE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Codeine is a prodrug that undergoes O-demethylation by CYP2D6 to morphine, which acts as a μ-opioid receptor agonist, inhibiting adenylate cyclase and modulating neurotransmitter release in the CNS. Acetaminophen inhibits cyclooxygenase (COX) enzymes, primarily in the CNS, reducing prostaglandin synthesis and modulating pain perception.
Acetaminophen: cyclooxygenase (COX) inhibitor, primarily central, analgesic and antipyretic. Aspirin: irreversible COX-1 and COX-2 inhibitor, analgesic, anti-inflammatory, antipyretic, antiplatelet. Codeine: prodrug converted to morphine; mu-opioid receptor agonist.
Management of mild to moderate pain where an opioid analgesic is needed
Mild to moderate pain,Fever (acetaminophen and aspirin),Inflammatory conditions (aspirin)
One or 2 tablets (acetaminophen 300 mg-codeine 60 mg per tablet) orally every 4 hours as needed for pain; maximum 12 tablets per day.
1-2 tablets (each containing acetaminophen 300 mg, aspirin 300 mg, codeine phosphate 30 mg) orally every 4-6 hours as needed for pain; maximum 8 tablets/day.
Codeine: Terminal half-life of 2.5-3.5 hours; however, its active metabolite morphine has a half-life of 1.5-2 hours, and morphine-6-glucuronide (M6G) has a half-life of 2-4 hours. Acetaminophen: Terminal half-life of 2-3 hours in adults; prolonged in hepatic impairment (up to 4-5 hours) or overdose (4-12 hours). Clinically, duration of analgesic effect is approximately 4-6 hours.
Acetaminophen: 2-3 hours (terminal). Aspirin: 15-30 minutes (parent drug); salicylate: 2-3 hours at low doses, 15-30 hours at high doses due to saturable metabolism. Codeine: 2.5-4 hours. Clinical context: Prolonged half-life of salicylate at high doses increases risk of toxicity; hepatic impairment prolongs acetaminophen and codeine half-lives.
Codeine: metabolized by CYP2D6 to morphine (active), CYP3A4 to norcodeine, and glucuronidation. Acetaminophen: extensively metabolized in the liver via conjugation (glucuronidation, sulfation) and minor oxidation by CYP2E1 to N-acetyl-p-benzoquinone imine (NAPQI), which is detoxified by glutathione.
Acetaminophen: hepatic via CYP2E1, CYP1A2, CYP3A4; glucuronidation and sulfation; NAPQI formation. Aspirin: hepatic hydrolysis to salicylate; conjugation with glycine and glucuronic acid. Codeine: hepatic via CYP2D6 to morphine (active); also via CYP3A4 to norcodeine.
Codeine and its metabolites (including morphine, morphine-6-glucuronide, and norcodeine) are primarily excreted renally. Approximately 90% of a codeine dose is excreted in urine within 24 hours, with 5-15% as free codeine, 5-13% as free morphine, 40-60% as codeine conjugates, and 5-10% as morphine conjugates. Fecal excretion accounts for less than 5%. Acetaminophen is primarily metabolized in the liver to glucuronide and sulfate conjugates; about 85% of a dose is excreted renally as conjugates within 24 hours, with 2-4% excreted unchanged. Minor biliary/fecal elimination occurs for both drugs.
Acetaminophen: renal excretion of metabolites (glucuronide and sulfate conjugates, ~85-90%), minor parent drug (<5%). Aspirin: renal excretion of salicylate and its metabolites (salicyluric acid, glucuronides, gentisic acid), dose-dependent; at therapeutic doses, ~50-80% as free salicylate and conjugates. Codeine: renal excretion of free and conjugated codeine (about 90%) and metabolites (morphine, norcodeine).
Codeine: Approximately 20-40% bound to plasma proteins (primarily albumin). Morphine: 20-35% bound. Acetaminophen: 10-25% bound to albumin. Binding is minimal and generally not clinically significant.
Acetaminophen: 10-25% (albumin). Aspirin: 50-80% (albumin), dose-dependent; salicylate: 75-90% (albumin). Codeine: ~7% (albumin).
Codeine: Vd approximately 3-4 L/kg (range 2.5-5 L/kg). Acetaminophen: Vd approximately 0.9 L/kg (range 0.7-1.0 L/kg). Codeine's larger Vd indicates extensive tissue distribution; acetaminophen distributes evenly throughout body fluids.
Acetaminophen: 0.9-1.0 L/kg (large distribution including liver). Aspirin: 0.15-0.2 L/kg (low Vd, confined to plasma and extracellular fluid); salicylate: 0.2-0.3 L/kg. Codeine: 3-6 L/kg (extensive tissue distribution). Clinical meaning: Large Vd for codeine suggests extensive tissue binding; aspirin Vd is small, consistent with limited extravascular distribution.
Oral: Codeine bioavailability is approximately 50-60% (first-pass metabolism). Acetaminophen bioavailability is 70-90% (absorbed rapidly from GI tract; first-pass metabolism minimal). Rectal bioavailability of acetaminophen is approximately 80-90% of oral.
Oral: Acetaminophen: 85-95%. Aspirin: 40-60% (due to first-pass hydrolysis to salicylate). Codeine: ~50% due to first-pass metabolism.
e GFR 30-50 m L/min: use with caution, reduce dose by 25%. e GFR <30 m L/min: not recommended due to risk of accumulation and respiratory depression.
GFR 30-59 m L/min: Administer every 6 hours; maximum 6 tablets/day. GFR 15-29 m L/min: Administer every 12 hours; maximum 4 tablets/day. GFR <15 m L/min: Not recommended due to accumulation of codeine metabolites.
Child-Pugh class A: caution, maximum 2 tablets per dose; class B or C: contraindicated.
Child-Pugh Class A: No adjustment. Child-Pugh Class B: Reduce dose by 50% and extend interval to every 6 hours; maximum 4 tablets/day. Child-Pugh Class C: Contraindicated.
Not recommended for children under 12 years. For ages 12-18: weight-based codeine dosing 0.5-1 mg/kg/dose every 4-6 hours (max 60 mg/dose); acetaminophen 15 mg/kg/dose every 4-6 hours (max 75 mg/kg/day). Use lowest effective dose.
Not recommended for children <12 years due to aspirin risk of Reye syndrome. For children ≥12 years: Dose based on codeine component (0.5-1 mg/kg/dose) with maximum acetaminophen 75 mg/kg/day and aspirin 100 mg/kg/day. Typical: 1 tablet (acetaminophen 300 mg/aspirin 300 mg/codeine 30 mg) every 4-6 hours as needed; max 4 tablets/day.
Initiate at half the adult dose (1 tablet) every 4 hours due to increased sensitivity to opioids and acetaminophen hepatotoxicity; maximum 8 tablets per day. Monitor renal and hepatic function closely.
Start with lowest effective dose (e.g., 1 tablet every 6 hours); monitor renal and hepatic function; maximum 6 tablets/day due to increased sensitivity and risk of adverse effects.
WARNING: ADDICTION, ABUSE, AND MISUSE; LIFE-THREATENING RESPIRATORY DEPRESSION; ACCIDENTAL INGESTION; ULTRA-RAPID METABOLISM OF CODEINE AND OTHER RISK FACTORS FOR LIFE-THREATENING RESPIRATORY DEPRESSION IN CHILDREN; NEONATAL OPIOID WITHDRAWAL SYNDROME; HEPATOTOXICITY; INTERACTION WITH ALCOHOL; RISKS FROM CONCOMITANT USE WITH BENZODIAZEPINES OR OTHER CNS DEPRESSANTS; RISK OF MEDICATION ERRORS.
Risk of medication errors: confusion between different strengths and concentrations of acetaminophen can result in accidental overdose and fatal hepatotoxicity. Aspirin use in children and teenagers with viral infections is associated with Reye's syndrome.
Risk of addiction, abuse, and misuse,Life-threatening respiratory depression, especially in patients with compromised respiratory function,Accidental ingestion of even one dose, especially by children, can be fatal,Ultra-rapid metabolism of codeine to morphine due to CYP2D6 polymorphism leading to toxicity,Neonatal opioid withdrawal syndrome with prolonged use during pregnancy,Hepatotoxicity due to acetaminophen, especially with doses >4000 mg/day or with concurrent alcohol use,Interaction with alcohol and other CNS depressants,Concomitant use with MAOIs or within 14 days is contraindicated,Avoid use in children <12 years of age and in children <18 years after tonsillectomy/adenoidectomy
Hepatotoxicity (acetaminophen dose >4 g/day), Reye's syndrome (aspirin in children), respiratory depression (codeine), tolerance/dependence, bleeding risk (aspirin), GI toxicity, renal impairment, hypersensitivity reactions.
Hypersensitivity to codeine, acetaminophen, or any component,Significant respiratory depression,Acute or severe bronchial asthma in an unmonitored setting or without resuscitative equipment,Known or suspected gastrointestinal obstruction, including paralytic ileus,Concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days,Children <12 years of age,Children <18 years of age after tonsillectomy/adenoidectomy
Hypersensitivity to any component, active peptic ulcer disease, bleeding disorders, severe hepatic impairment, severe respiratory depression, children with viral illness (aspirin), pregnancy (third trimester for aspirin, codeine cautious).
Avoid alcohol and foods containing alcohol (e.g., desserts, sauces) due to increased risk of hepatotoxicity and CNS depression. No specific food restrictions otherwise.
Avoid alcohol due to increased risk of acetaminophen hepatotoxicity and aspirin-induced GI bleeding. Avoid large amounts of caffeine or high-tyramine foods (e.g., aged cheeses, cured meats) as they may affect CYP2D6 metabolism of codeine.
Pregnancy Category C prior to 2015; current data insufficient for definitive risk. Acetaminophen: no consistent evidence of major malformations; codeine: opioid use in first trimester associated with small increased risk of neural tube defects (OR 1.1-1.3); third trimester use may cause neonatal opioid withdrawal syndrome (NOWS) and respiratory depression at delivery.
Acetaminophen: Generally considered low risk; association with ASD and ADHD with prolonged use not fully established. Aspirin: First trimester: possible increased risk of gastroschisis; second trimester: relatively safe; third trimester: risk of premature closure of ductus arteriosus, oligohydramnios, and increased peripartum hemorrhage. Codeine: First trimester: possible neural tube defects; second and third trimesters: risk of respiratory depression, withdrawal in neonate with chronic use; neonatal opioid withdrawal syndrome (NOWS) possible.
Acetaminophen is compatible (low levels in milk). Codeine is present in milk; M/P ratio approximately 2:1 (morphine). Caution: ultra-rapid CYP2D6 metabolizers may produce high morphine levels leading to infant toxicity. Use lowest effective dose for shortest duration; monitor infant for drowsiness, difficulty breathing.
Acetaminophen: M/P ratio approximately 0.91-1.42; considered safe. Aspirin: M/P ratio 0.08-0.15; high doses may cause Reye's syndrome; avoid or use low doses. Codeine: M/P ratio about 2.5; variable metabolism; risk of CNS depression in infant; avoid due to potential for toxicity in CYP2D6 ultrarapid metabolizers.
No specific dose adjustment recommended for acetaminophen; codeine pharmacokinetics altered in pregnancy (increased clearance, decreased half-life). Avoid codeine in pregnancy if possible; if used, lowest effective dose for shortest duration. Consider alternative analgesics (e.g., acetaminophen alone). Postpartum: resume standard dosing.
Acetaminophen: No dose adjustment needed. Aspirin: Avoid in third trimester; use lowest effective dose if necessary. Codeine: Avoid in pregnancy; if used, lowest effective dose for shortest duration; caution for CYP2D6 polymorphism. Pharmacokinetic changes: Increased clearance of codeine during pregnancy may require higher doses but risk outweighs benefit.
Each tablet contains acetaminophen 300 mg and codeine phosphate 60 mg. Maximum acetaminophen dose: 4 g/day; avoid other acetaminophen-containing products. Codeine is a prodrug; CYP2D6 poor metabolizers may have reduced efficacy, while ultra-rapid metabolizers risk toxicity. Monitor for respiratory depression, especially in opioid-naive patients. Use with caution in patients with liver impairment or G6PD deficiency.
Combination analgesic with acetaminophen (hepatotoxic at high doses), aspirin (antiplatelet, GI irritant, contraindicated in children <12 due to Reye's syndrome), and codeine (prodrug to morphine via CYP2D6; efficacy depends on CYP2D6 phenotype; risk of CNS/respiratory depression). Avoid in severe hepatic/renal impairment, active peptic ulcer, bleeding disorders, or concomitant use of other CNS depressants. Maximum acetaminophen dose from all sources: 4 g/day.
Do not exceed 12 tablets in 24 hours due to acetaminophen content.,Avoid alcohol while taking this medication.,This drug may cause drowsiness; do not drive or operate machinery until you know how it affects you.,Contact your doctor if you experience signs of allergic reaction (rash, difficulty breathing) or liver injury (yellowing of skin/eyes, dark urine).,Do not take with other products containing acetaminophen (e.g., Tylenol, cold medicines).,Codeine can be habit-forming; use only as prescribed.,Women who are breastfeeding should consult their doctor; codeine can pass into breast milk.
Do not exceed recommended dose; acetaminophen overdosage can cause serious liver damage.,Do not take with other products containing acetaminophen or aspirin.,Avoid alcohol while taking this medication to reduce risk of liver toxicity and GI bleeding.,This product contains aspirin; do not give to children/teenagers with chickenpox or flu-like symptoms to avoid Reye's syndrome.,May cause drowsiness; do not drive or operate machinery until you know how you react.,Codeine is a narcotic pain reliever with abuse potential; use exactly as prescribed.,Seek medical attention if you experience signs of allergic reaction (rash, difficulty breathing) or bleeding (black/tarry stools, unusual bruising).
"Pirenzepine, a selective M1 muscarinic antagonist, reduces gastrointestinal motility and secretions, while codeine, an opioid agonist, also decreases gastrointestinal motility via mu-opioid receptors. Concurrent use leads to additive anticholinergic and opioid effects, resulting in enhanced risk of severe constipation, paralytic ileus, and central nervous system depression. Clinically, patients may experience exacerbated sedation, respiratory depression, and urinary retention."
"Ropinirole, a non-ergoline dopamine agonist used in Parkinson's disease and restless legs syndrome, may reduce the analgesic efficacy of codeine. This is likely due to pharmacodynamic antagonism at central dopamine and opioid receptors, as well as potential pharmacokinetic interactions that decrease the conversion of codeine to its active metabolite morphine via CYP2D6 inhibition by ropinirole. The resultant blunted opioid response can lead to inadequate pain control, necessitating dose adjustment or alternative therapy."
"Vemurafenib induces CYP3A4, significantly reducing the plasma concentrations of codeine, which is metabolized via CYP3A4 to its active metabolite morphine. This may diminish codeine's analgesic efficacy, potentially leading to inadequate pain control. Additionally, reduced formation of morphine may lower the risk of opioid-related adverse effects."
"Pirenzepine, a selective M1 muscarinic antagonist, reduces gastrointestinal motility and secretions, while codeine, an opioid agonist, also decreases gastrointestinal motility via mu-opioid receptors. Concurrent use leads to additive anticholinergic and opioid effects, resulting in enhanced risk of severe constipation, paralytic ileus, and central nervous system depression. Clinically, patients may experience exacerbated sedation, respiratory depression, and urinary retention."
"Ropinirole, a non-ergoline dopamine agonist used in Parkinson's disease and restless legs syndrome, may reduce the analgesic efficacy of codeine. This is likely due to pharmacodynamic antagonism at central dopamine and opioid receptors, as well as potential pharmacokinetic interactions that decrease the conversion of codeine to its active metabolite morphine via CYP2D6 inhibition by ropinirole. The resultant blunted opioid response can lead to inadequate pain control, necessitating dose adjustment or alternative therapy."
"Vemurafenib induces CYP3A4, significantly reducing the plasma concentrations of codeine, which is metabolized via CYP3A4 to its active metabolite morphine. This may diminish codeine's analgesic efficacy, potentially leading to inadequate pain control. Additionally, reduced formation of morphine may lower the risk of opioid-related adverse effects."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about TYLENOL W/ CODEINE NO. 4 vs ACETAMINOPHEN, ASPIRIN, AND CODEINE PHOSPHATE, answered by our medical review team.
TYLENOL W/ CODEINE NO. 4 is a Opioid Agonist that works by Codeine is a prodrug that undergoes O-demethylation by CYP2D6 to morphine, which acts as a μ-opioid receptor agonist, inhibiting adenylate cyclase and modulating neurotransmitter release in the CNS. Acetaminophen inhibits cyclooxygenase (COX) enzymes, primarily in the CNS, reducing prostaglandin synthesis and modulating pain perception.. ACETAMINOPHEN, ASPIRIN, AND CODEINE PHOSPHATE is a Opioid Agonist that works by Acetaminophen: cyclooxygenase (COX) inhibitor, primarily central, analgesic and antipyretic. Aspirin: irreversible COX-1 and COX-2 inhibitor, analgesic, anti-inflammatory, antipyretic, antiplatelet. Codeine: prodrug converted to morphine; mu-opioid receptor agonist.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between TYLENOL W/ CODEINE NO. 4 and ACETAMINOPHEN, ASPIRIN, AND CODEINE PHOSPHATE depend on the specific clinical indication. These are both Opioid Agonist agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of TYLENOL W/ CODEINE NO. 4 is: One or 2 tablets (acetaminophen 300 mg-codeine 60 mg per tablet) orally every 4 hours as needed for pain; maximum 12 tablets per day.. The standard adult dose of ACETAMINOPHEN, ASPIRIN, AND CODEINE PHOSPHATE is: 1-2 tablets (each containing acetaminophen 300 mg, aspirin 300 mg, codeine phosphate 30 mg) orally every 4-6 hours as needed for pain; maximum 8 tablets/day.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
A moderate-severity drug interaction has been identified when combining TYLENOL W/ CODEINE NO. 4 and ACETAMINOPHEN, ASPIRIN, AND CODEINE PHOSPHATE. Codeine, a prodrug converted to morphine via CYP2D6, and metyrosine, a tyrosine hydroxylase inhibitor, synergistically depress the central nervous system. Codeine's mu-opioid receptor agonism and metyrosine's reduction of catecholamine synthesis lead to enhanced sedation, respiratory depression, and hypotension. Clinically, patients may experience excessive drowsiness, confusion, or respiratory compromise, particularly at higher doses or in vulnerable populations. Consult your prescriber before combining these medications.
The maternal-fetal safety profiles differ. TYLENOL W/ CODEINE NO. 4 is classified as Category D/X. Pregnancy Category C prior to 2015; current data insufficient for definitive risk. Acetaminophen: no consistent evidence of major malformations; codeine: opioid use in first trimes. ACETAMINOPHEN, ASPIRIN, AND CODEINE PHOSPHATE is classified as Category D/X. Acetaminophen: Generally considered low risk; association with ASD and ADHD with prolonged use not fully established. Aspirin: First trimester: possible increased risk of gastrosch. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.