Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
TYLENOL W/ CODEINE NO. 1 vs 8-HOUR BAYER
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 via CYP2D6 to morphine, which acts as a μ-opioid receptor agonist. Acetaminophen inhibits cyclooxygenase (COX) enzymes in the CNS, reducing prostaglandin synthesis and modulating pain perception.
Irreversibly acetylates cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), inhibiting prostaglandin and thromboxane A2 synthesis, leading to analgesic, antipyretic, anti-inflammatory, and antiplatelet effects.
Mild to moderate pain,Pyrexia
Relief of pain, fever, and inflammation,Reduction of risk of myocardial infarction in patients with previous MI or unstable angina,Prevention of recurrent ischemic stroke or transient ischemic attack
Adult: 1-2 tablets (acetaminophen 300 mg/codeine 8 mg per tablet) orally every 4-6 hours as needed; maximum 8 tablets per day. Route: oral. Frequency: every 4-6 hours.
325-650 mg every 8 hours for pain/fever; 81-325 mg daily for cardiovascular prophylaxis.
Acetaminophen: 2-3 hours; Codeine: 2.5-3.5 hours; Morphine (active metabolite): 2-4 hours. Terminal half-life prolonged in hepatic impairment or elderly.
15-20 hours (terminal elimination half-life) for salicylate at therapeutic concentrations; prolonged to 20-30 hours at high doses due to saturation of hepatic metabolism (zero-order kinetics).
Acetaminophen is primarily metabolized via glucuronidation and sulfation in the liver, with a minor pathway via CYP2E1 to a toxic metabolite (NAPQI). Codeine is metabolized via CYP2D6 to morphine, via CYP3A4 to norcodeine, and via glucuronidation.
Hepatic hydrolysis by esterases to salicylic acid, which is primarily conjugated in the liver via glucuronidation and glycine conjugation (salicyluric acid), with minor oxidation by cytochrome P450 (CYP2C9) to gentisic acid.
Renal: ~70-80% of codeine as inactive metabolites (codeine-6-glucuronide, norcodeine, morphine) and ~5-10% as unchanged codeine; ~5-15% of acetaminophen as unchanged drug. Biliary/fecal: minimal (<5% for both).
Renal excretion of conjugated salicylate metabolites (75% as salicyluric acid, 10% as salicyl phenolic glucuronide, 5% as salicyl acyl glucuronide, 5% as gentisic acid); 10% free salicylate; approximately 10% eliminated in feces via bile.
Acetaminophen: 10-25% bound to plasma proteins; Codeine: ~25% bound to plasma proteins.
80-90% bound to albumin; binding is concentration-dependent and saturable.
Acetaminophen: ~0.9 L/kg (distributes throughout total body water); Codeine: ~3-6 L/kg (extensively distributed into tissues).
0.15-0.2 L/kg for salicylate; distributes into synovial fluid, CNS, and placental tissues; Vd increases in acidosis.
Acetaminophen: oral bioavailability ~80-85%; Codeine: oral bioavailability ~60-90% (due to first-pass metabolism to morphine).
Oral: Approximately 100% for immediate-release, but extended-release may have slightly reduced absorption (relative bioavailability 85-90% compared to immediate-release).
Cr Cl 30-50 m L/min: Administer every 6 hours; Cr Cl <30 m L/min: Avoid due to risk of codeine accumulation and toxicity; hemodialysis: Not recommended.
Avoid in severe renal impairment (Cr Cl <30 m L/min). Use with caution and monitor for bleeding in moderate impairment. Reduce dose or extend interval.
Child-Pugh Class A (mild): No adjustment needed; Child-Pugh Class B (moderate): Reduce dose by 50% and extend interval to every 6-8 hours; Child-Pugh Class C (severe): Contraindicated.
Avoid in severe hepatic impairment. Use with caution in moderate impairment; monitor liver function.
Weight-based: Codeine not recommended in pediatric patients <12 years due to risk of respiratory depression; for ages 12-18 years: 1 tablet (acetaminophen 300 mg/codeine 8 mg) orally every 4-6 hours as needed; maximum 4 tablets per day.
Not recommended in children <12 years for viral infections due to Reye's syndrome risk (contraindicated).
Start at lowest effective dose (1 tablet) and monitor for respiratory depression and constipation; consider acetaminophen 300 mg/codeine 8 mg every 6 hours; maximum 4 tablets per day.
Increased risk of GI bleeding and renal impairment; use lowest effective dose, monitor renal function and signs of bleeding.
WARNING: RISK OF MEDICATION ERRORS; ADDICTION, ABUSE, AND MISUSE; RESPIRATORY DEPRESSION; ACCIDENTAL INGESTION; ULTRA-RAPID METABOLISM OF CODEINE AND OTHER RISK FACTORS FOR LIFE-THREATENING RESPIRATORY DEPRESSION IN CHILDREN; NEONATAL OPIOID WITHDRAWAL SYNDROME; INTERACTION WITH ALCOHOL; RISKS FROM CONCOMITANT USE WITH BENZODIAZEPINES OR OTHER CNS DEPRESSANTS; HEPATOTOXICITY.
None
Risk of medication errors (confusion with other products),Addiction, abuse, and misuse,Life-threatening respiratory depression,Accidental ingestion (especially in children),Ultra-rapid metabolism of codeine (CYP2D6 ultra-rapid metabolizers),Neonatal opioid withdrawal syndrome with prolonged use during pregnancy,Hepatotoxicity (acetaminophen overdose),Severe hypotension,Seizures,Adrenal insufficiency,Serotonin syndrome with concomitant serotonergic drugs,Increased risk of severe skin reactions (e.g., SJS/TEN),Interaction with alcohol,Risks from concomitant use with benzodiazepines or other CNS depressants,Impaired mental/physical abilities,Use in children with respiratory conditions,Hepatic or renal impairment
Increased risk of gastrointestinal bleeding and ulceration; Reye syndrome in children with viral illness; Hemorrhagic stroke risk with high doses; Impaired renal function in predisposed patients; Bronchospasm in aspirin-sensitive asthma; Anaphylactic reactions; Use caution in patients with hepatic impairment or G6PD deficiency.
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,Patients with severe hepatic impairment or acute liver disease,Postoperative pain management in children who have had tonsillectomy and/or adenoidectomy,Concurrent use of monoamine oxidase inhibitors (MAOIs) or within 14 days of such therapy
Known hypersensitivity to NSAIDs or aspirin; Active peptic ulcer disease or GI bleeding; Severe renal impairment (e GFR <30 m L/min); Hemorrhagic diathesis; Children with viral infection (Reye syndrome); Third trimester of pregnancy; Severe hepatic impairment.
Avoid alcohol; may increase risk of hepatotoxicity and CNS depression. No specific food restrictions. May be taken with food to reduce gastrointestinal upset.
Avoid alcohol; may increase risk of gastrointestinal bleeding. No specific food restrictions, but taking with food can reduce gastric irritation. Avoid high-dose vitamin C supplements as they may increase salicylate levels.
Acetaminophen: Low teratogenic risk; use at therapeutic doses not associated with increased major malformations. Codeine: First trimester: Risk of malformations unclear; some studies suggest small increased risk of respiratory defects and spina bifida. Third trimester: Prolonged use may cause neonatal opioid withdrawal syndrome (NOWS); high doses near term may cause neonatal respiratory depression. Avoid chronic high doses.
First trimester: No well-controlled studies. Avoid use unless clearly needed. Second and third trimesters: Aspirin should be avoided due to risk of premature closure of ductus arteriosus, oligohydramnios, and increased risk of maternal and fetal bleeding. High doses may cause constriction of ductus arteriosus in utero and persistent pulmonary hypertension in newborn.
Acetaminophen: Compatible; low levels in breast milk (M/P ratio ~0.91). Codeine: Excreted into breast milk; M/P ratio ~2.5. Risk of infant opioid toxicity, especially in ultra-rapid CYP2D6 metabolizers. Use lowest effective dose for shortest duration. Monitor infant for drowsiness, feeding difficulties, respiratory depression.
Small amounts of aspirin are excreted in breast milk. M/P ratio not established. Use with caution in breastfeeding women; avoid high doses due to risk of Reye's syndrome in infants and potential for adverse effects on platelet function.
No standard dose adjustment required for acetaminophen. Codeine: Increased clearance in pregnancy may require dose adjustment; however, use lowest effective dose due to unpredictable metabolism. Avoid codeine in pregnancy if possible. Maximum recommended dose: acetaminophen 3000 mg/day; codeine 60 mg/day.
Pregnancy increases clearance of aspirin; however, dose adjustments are not routinely recommended due to narrow therapeutic index. Use lowest effective dose for shortest duration. Avoid in third trimester.
Contains 300 mg acetaminophen and 15 mg codeine per tablet. Maximum acetaminophen dose 4000 mg/day; avoid combination with other acetaminophen products. Codeine is a prodrug requiring CYP2D6 conversion to morphine; poor metabolizers have reduced analgesia, ultra-rapid metabolizers risk toxicity. Monitor for respiratory depression, especially in children, elderly, or obese. Not recommended in breastfeeding mothers due to risk of infant toxicity.
8-Hour Bayer is enteric-coated aspirin designed for extended release, reducing gastrointestinal irritation. Onset of action is delayed; not suitable for acute pain or rapid antiplatelet effect. Use with caution in patients with history of peptic ulcer disease or on anticoagulants. Monitor renal function in elderly or dehydrated patients. Avoid in children with viral illness due to Reye's syndrome risk.
Do not exceed 13 tablets per 24 hours due to acetaminophen limit.,Avoid alcohol while taking this medication.,Do not use with any other products containing acetaminophen or codeine.,May cause drowsiness; avoid driving or operating machinery.,Store out of reach of children and dispose of unused medication properly.,Seek medical help if you experience difficulty breathing, severe drowsiness, or signs of allergic reaction.
Take with a full glass of water; do not crush or chew the tablet.,Do not use within 7 days before surgery due to bleeding risk.,If used for pain, consult a doctor if symptoms persist for more than 10 days.,Avoid alcohol while taking this medication to reduce stomach bleeding risk.,Seek medical attention for signs of bleeding (black stools, blood in vomit).
"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."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about TYLENOL W/ CODEINE NO. 1 vs 8-HOUR BAYER, answered by our medical review team.
TYLENOL W/ CODEINE NO. 1 is a Opioid Agonist that works by Codeine is a prodrug that undergoes O-demethylation via CYP2D6 to morphine, which acts as a μ-opioid receptor agonist. Acetaminophen inhibits cyclooxygenase (COX) enzymes in the CNS, reducing prostaglandin synthesis and modulating pain perception.. 8-HOUR BAYER is a NSAID that works by Irreversibly acetylates cyclooxygenase-1 (COX-1) and cyclooxygenase-2 (COX-2), inhibiting prostaglandin and thromboxane A2 synthesis, leading to analgesic, antipyretic, anti-inflammatory, and antiplatelet effects.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between TYLENOL W/ CODEINE NO. 1 and 8-HOUR BAYER depend on the specific clinical indication. These are agents from distinct pharmacological classes 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. 1 is: Adult: 1-2 tablets (acetaminophen 300 mg/codeine 8 mg per tablet) orally every 4-6 hours as needed; maximum 8 tablets per day. Route: oral. Frequency: every 4-6 hours.. The standard adult dose of 8-HOUR BAYER is: 325-650 mg every 8 hours for pain/fever; 81-325 mg daily for cardiovascular prophylaxis.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between TYLENOL W/ CODEINE NO. 1 and 8-HOUR BAYER in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. TYLENOL W/ CODEINE NO. 1 is classified as Category D/X. Acetaminophen: Low teratogenic risk; use at therapeutic doses not associated with increased major malformations. Codeine: First trimester: Risk of malformations unclear; some studi. 8-HOUR BAYER is classified as Category C. First trimester: No well-controlled studies. Avoid use unless clearly needed. Second and third trimesters: Aspirin should be avoided due to risk of premature closure of ductus arte. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.