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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

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

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.

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.

About this calculation · Accuracy & Methodology

Key Terms

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.

Real-World Examples

Example 1

Ibuprofen — Child Fever

Patient: 8 years old, 55 lbs (25 kg). Dose: 25 kg × 5–10 mg/kg = 125–250 mg.

Liquid: Children's Motrin 100 mg/5 mL → 6.25–12.5 mL (1¼–2½ tsp). Max daily: 25 × 40 = 1000 mg. Dose every 6–8 hours.

Example 2

Acetaminophen — Adult Headache

Patient: Adult, 160 lbs. Standard adult dose: 500–1000 mg.

Max daily: 3000 mg (6 doses of 500 mg). Check all other medications for hidden acetaminophen content. Every 4–6 hours as needed.

Example 3

Naproxen — Adult Back Pain (Schedule Planning)

Patient: Adult, 185 lbs. Took first dose (220 mg) at 8:00 AM.

Next safe dose: 4:00 PM (8-hr min) to 8:00 PM (12-hr ideal). Max 660 mg/day (3 doses). Max 5 days OTC. Use the Dose Planner tab to track this automatically.

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.

Frequently Asked Questions

Can I give ibuprofen and acetaminophen together?
Yes — alternating ibuprofen and acetaminophen is evidence-supported. They work by different mechanisms, don't interact, and alternating allows more continuous coverage. A common schedule: acetaminophen at hour 0, ibuprofen at hour 4–6, acetaminophen again at hour 8. Never exceed either drug's individual maximum daily dose.
Why choose naproxen (Aleve) over ibuprofen?
Naproxen's primary advantage is its 8–12 hour dosing interval vs. ibuprofen's 4–6 hours. This makes it more convenient for chronic pain (back pain, arthritis, menstrual cramps) where you need round-the-clock relief with fewer doses. The trade-off: slightly slower onset (30–60 min vs. 20–30 min) and not approved OTC for children under 12.
What is Reye's syndrome?
A rare but potentially fatal condition causing rapid liver failure and brain swelling in children and teenagers after viral infections (especially influenza and chickenpox) when aspirin is used. Since the 1980s warning, Reye's syndrome has become extremely rare — but the risk means aspirin should NEVER be given to anyone under 18 without explicit physician guidance.
Why can't infants under 6 months have ibuprofen?
Immature kidney development in infants under 6 months makes ibuprofen clearance significantly slower, increasing the risk of renal toxicity. Acetaminophen is the appropriate fever and pain reliever for this age group, using weight-based dosing with infant formulations.
How accurate must the weight be for child dosing?
Very accurate — a 10% weight error translates directly to a 10% dosing error. Use a recent actual measurement, not a guess. For liquid doses, always use the measuring device included with the medication, never a kitchen spoon (which is inaccurate by up to 20%).
Can Benadryl be used as a sleep aid?
Diphenhydramine is the active ingredient in most OTC sleep aids (ZzzQuil, Unisom). It's effective short-term for occasional sleeplessness, but tolerance develops within 3–5 nights. Chronic use in adults over 65 has been associated with cognitive concerns. Don't use it as a regular sleep aid without consulting a doctor.
How many days can I use OTC pain relievers?
Ibuprofen and acetaminophen: max 10 days for pain, 3 days for fever without medical guidance. Naproxen: max 5 days for pain, 3 days for fever. Aspirin: max 10 days for pain. If symptoms persist beyond these limits, see a doctor — continued symptoms may indicate a condition requiring proper diagnosis.