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OTC Drug Dosage Calculator

Weight-based dosing for 5 common OTC medications. Safety gauge, dose planner, and interaction guide. For informational purposes only — always consult a healthcare provider.

Medication
Patient Type
Typical adult: 120–220 lbs
⚕️ For informational reference only. Always read package labels and consult a pharmacist or physician before medicating.
Recommended Dose
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Enter weight to calculate
Dose Safety Gauge
Safe Max — OF DAILY MAX
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Single Dose
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Max Daily
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Interval
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Liquid Dose
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Teaspoon
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Dose Rate
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Onset
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Duration
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Adult Dose by Body Weight — All Medications
Chart: adult dose by body weight — all medications.

Current weight column highlighted. Dashed lines = maximum single dose per medication. Chart shows adult standard doses.

⚕ Always follow your prescriber's instructions. Do not change medication doses without consulting your doctor or pharmacist.

Dosage by Weight — Ibuprofen
Weight (lbs) Weight (kg) Patient Single Dose Max Daily Interval Liquid (mL / tsp)
Can I Combine These Medications?

Based on pharmacological interactions. Always confirm with a pharmacist for your specific situation.

Ibuprofen Acetaminophen Naproxen Benadryl Aspirin
Ibuprofen—✓ OK✗ NO✓ OK✗ NO
Acetaminophen✓ OK—✓ OK✓ OK⚠ WARN
Naproxen✗ NO✓ OK—✓ OK✗ NO
Benadryl✓ OK✓ OK✓ OK—✓ OK
Aspirin✗ NO⚠ WARN✗ NO✓ OK—
✓ OK — Different mechanisms, no interaction ✗ NO — Same class or harmful interaction ⚠ WARN — Use caution, consult pharmacist
Drug Interactions & Warnings
Ibuprofen (Advil/Motrin)
  • Do not combine with aspirin, naproxen, or other NSAIDs — doubles GI/kidney risk without added benefit
  • Aspirin: ibuprofen blocks aspirin's antiplatelet effect — critical for cardiac patients
  • Warfarin / blood thinners: significantly increased bleeding risk
  • ACE inhibitors / diuretics: reduced effectiveness, kidney strain
  • SSRIs (Prozac, Zoloft): increased GI bleeding risk when combined
Acetaminophen (Tylenol)
  • Alcohol: even 3 drinks/day significantly increases liver damage risk
  • Warfarin: acetaminophen enhances warfarin's blood-thinning effect
  • Other acetaminophen products: cold/flu medicines often contain hidden Tylenol — check all labels
  • Isoniazid (TB treatment): increases liver toxicity risk
Naproxen (Aleve)
  • Do not combine with ibuprofen, aspirin, or other NSAIDs — same class
  • Warfarin: significantly increased bleeding risk
  • Lithium: naproxen can raise lithium levels to toxic range
  • Methotrexate: naproxen can raise methotrexate levels
  • ACE inhibitors: reduced blood pressure control, kidney risk
Diphenhydramine (Benadryl)
  • Do not combine with other antihistamines, sleep aids, or sedatives — extreme drowsiness
  • Alcohol: dangerous CNS depression, respiratory risk
  • Opioids: increased sedation and respiratory depression risk
  • MAOIs: severe interaction — do not use within 14 days of MAOIs
  • Elderly patients: higher sensitivity to anticholinergic effects (confusion, falls)
Aspirin (Bayer)
  • NEVER give to children or teenagers — Reye's syndrome risk
  • Warfarin: severe bleeding risk — requires monitoring
  • Ibuprofen/naproxen: doubles NSAID risk; ibuprofen blocks aspirin's heart protection
  • SSRIs: increased GI bleeding risk
  • Methotrexate: aspirin raises methotrexate blood levels
⚠ Seek Emergency Care Immediately If You Notice:
Allergic Reaction
Hives, swelling of face/lips/tongue/throat, difficulty breathing, anaphylaxis — call 911
Overdose / Too Much
Nausea, vomiting, stomach pain. Tylenol overdose can be fatal even without immediate symptoms — call Poison Control: 1-800-222-1222
GI Bleeding (NSAIDs)
Vomiting blood or material that looks like coffee grounds, dark/tarry stools, severe abdominal pain
No Improvement
Fever above 103°F (39.4°C), pain lasting more than 10 days, or new/worsening symptoms — see a doctor
Schedule Setup
Select a medication and enter your first dose time to see your schedule.
⚕️ This planner is a reference tool. Always follow official product labeling and consult your pharmacist for personal guidance.
Next Safe Window
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Doses Taken Today
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Doses Remaining
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Daily Total (mg)
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Daily Dose Used —
Next Safe Dose In
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Enter first dose time to see countdown
24-Hour Dose Timeline
Too Soon Caution Window Safe to Take Dose Taken
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How to Use This Calculator

1

Choose Your Medication

Select from 5 OTC medications using the color-coded chips. Each has its own safety profile, dosing interval, and age restrictions.

2

Enter Patient Details

Toggle Adult or Child mode. Enter body weight in lbs or kg. For children, enter age to catch age-based contraindications automatically.

3

Read the Dose & Safety Gauge

The hero result shows the recommended single dose. The safety gauge shows where one dose falls relative to the daily maximum — green is safe, red means you're near the limit.

4

Plan Your Schedule

Use the Dose Planner tab to enter your first dose time and see a live 24-hour timeline showing your next safe dose windows with a live countdown.

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Formula & Methodology

Pediatric Weight-Based Dose

Dose (mg) = Weight (kg) × mg/kg rate

For children, dose is calculated proportionally by weight. Example: A 20 kg child receiving ibuprofen at 5–10 mg/kg gets 100–200 mg per dose.

Liquid Volume Calculation

Volume (mL) = Dose (mg) ÷ Concentration (mg/mL)

Children's ibuprofen suspension: 100 mg/5 mL (20 mg/mL). Children's Tylenol: 160 mg/5 mL (32 mg/mL). Children's Benadryl: 12.5 mg/5 mL (2.5 mg/mL). 5 mL = 1 teaspoon.

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Key Terms Explained

mg/kg Dosing — Dose calculated by body weight in milligrams per kilogram — ensures proportional dosing for children of all sizes.
NSAID — Non-Steroidal Anti-Inflammatory Drug. Ibuprofen, naproxen, and aspirin are NSAIDs. They reduce pain, fever, and inflammation by inhibiting COX enzymes.
Analgesic — A pain-relieving medication. All five medications covered here are analgesics.
Antipyretic — A fever-reducing medication. Ibuprofen, acetaminophen, naproxen, and aspirin are antipyretics. Benadryl is not.
Antihistamine — A medication that blocks histamine receptors. Benadryl (diphenhydramine) is a first-generation antihistamine that also causes drowsiness.
Half-Life — Time for the body to eliminate half of a dose. Naproxen has the longest half-life (12–17 hrs), which is why it dosed every 8–12 hours vs. ibuprofen's 4–6 hours.
OTC — Over-the-counter — medications available without a prescription. This calculator covers OTC doses only. Prescription formulations may differ.
Reye's Syndrome — A rare but potentially fatal condition causing liver failure and brain swelling in children after viral illness when aspirin is used. This is why aspirin is contraindicated in anyone under 18.
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Real-World Examples

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Sarah

Ibuprofen — Child Fever

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Safe OTC Medication Practices

Why Weight-Based Dosing Matters for Children

A fixed dose that is safe for a 40 kg child could cause toxicity in a 15 kg toddler. Weight-based dosing ensures every child gets the right amount regardless of size. For pediatric patients, always use a recent actual weight measurement — never estimate — and use the measuring device that comes with the medication.

The 5 OTC Medications Covered Here

Ibuprofen (Advil, Motrin) is an NSAID effective for pain, fever, and inflammation. Fast onset (20–30 min), every 4–6 hours dosing. Not for infants under 6 months. Acetaminophen (Tylenol) is a non-NSAID analgesic/antipyretic safe from birth. The liver-friendly choice — but liver-damaging with alcohol or overdose. Naproxen (Aleve) is a long-acting NSAID with 8–12 hour dosing — ideal for arthritis and chronic pain. Not OTC for children under 12. Diphenhydramine (Benadryl) is an antihistamine for allergies, hives, and itching. Causes significant drowsiness. Aspirin (Bayer) is an NSAID and antiplatelet agent — useful in adults but absolutely contraindicated in children under 18 due to Reye's syndrome risk.

Combining Medications Safely

The one evidence-supported combination is alternating ibuprofen and acetaminophen for fever or pain management — they work by different mechanisms and don't interact. Never combine two NSAIDs (ibuprofen + naproxen + aspirin in any combination). Use the Reference Guide tab's combination matrix to check any pairing.

This Calculator Is for Educational Reference Only

This tool provides general reference information based on standard OTC labeling and clinical guidelines. Actual doses may vary based on your specific product formulation, other medications you take, medical history, and individual factors. Always read the full product label and consult a pharmacist or physician before administering medication.

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Frequently Asked Questions

Can I take ibuprofen and acetaminophen at the same time?+

Yes, alternating ibuprofen and acetaminophen is safe and evidence-supported because they work by different mechanisms. A common schedule is acetaminophen at hour 0, ibuprofen at hour 4-6, then acetaminophen again at hour 8. Never exceed either drug's individual daily maximum.

Why does this calculator use weight-based dosing instead of a flat dose?+

Weight-based dosing provides more accurate and safer doses, especially for children and smaller adults. A 100 lb person and a 250 lb person have very different medication needs. The calculator uses mg/kg dosing guidelines from clinical pharmacology references to determine the optimal dose for your body weight.

What is the maximum safe daily dose of Tylenol (acetaminophen)?+

The absolute maximum is 4,000 mg/day for healthy adults, but most guidelines now recommend 3,000 mg/day as a practical safe limit. For people who drink alcohol regularly, are elderly, or have liver concerns, the limit drops to 2,000 mg/day. Remember that many cold and flu products contain hidden acetaminophen.

At what age can children safely take ibuprofen?+

Ibuprofen is approved for children 6 months and older. Infants under 6 months have immature kidneys that cannot safely process ibuprofen. For younger infants, acetaminophen (Tylenol) is the recommended OTC option for pain and fever, dosed carefully by weight.

Should I take OTC pain relievers with food?+

NSAIDs like ibuprofen, naproxen, and aspirin should be taken with food or milk to reduce stomach irritation and the risk of GI bleeding. Acetaminophen can be taken with or without food since it does not irritate the stomach lining. Always follow with a full glass of water.