💊 Drug Half-Life Calculator
Calculate how much of a drug remains in your body over time. Enter the drug's half-life and initial dosage to see the elimination curve across multiple half-life cycles.
📊 Drug Elimination Table
What Is the Half-Life of a Drug?
In pharmacology, the half-life of a drug describes the amount of time it takes for the drug's concentration in the blood plasma to reduce by half. It is one of the most important pharmacokinetic properties that helps clinicians assess the potency and toxicity of a drug over a given amount of time.
If we know the elimination time, we can easily evaluate how often the drug should be administered to maximize its effect and minimize adverse reactions. The concentration of a drug at a given moment is particularly crucial for medications with a narrow therapeutic range — such as drugs that can prolong the patient's QT interval and lead to heart arrhythmias.
How to Calculate Drug Half-Life
Our drug elimination half-life calculator uses the following equation:
Where:
- T — Half-life of the drug
- t — Time that has passed since the first administration of the drug
- Dosage(t) — Amount of drug present in a patient's body after time t
- Dosage(0) — Amount of drug administered at the very beginning
How to Use This Calculator
- Half-life — Enter the half-life of the drug in minutes, hours, or days. You can also click a drug from the quick-pick chips above.
- Dosage — Enter the amount of drug administered at the start.
- The results table will show at least 5 half-life cycles with the time elapsed, remaining dosage, and concentration as a percentage of the original.
Half-Life of Medication — Examples
Below is a reference table of common medications and their approximate half-lives:
| Drug | Half-Life |
|---|---|
| Acetaminophen | 1–4 h |
| Adderall | 9–14 h |
| Amiodarone | 26–107 days |
| Carbamazepine | 14–47 h |
| Ciprofloxacin | 4 h |
| Diazepam | 21–37 h |
| Digoxin | 36–48 h |
| Epinephrine | 2–3 min |
| Fentanyl | 3–12 h |
| Fluconazole | 20–50 h |
| Ganciclovir | 3–6 h |
| Haloperidol | 14–41 h |
| Heparin | 3–6 h |
| Ketoconazole | 2–8 h |
| Lidocaine | 1–2 h |
| Methotrexate | 3–10 h |
| Metronidazole | 8 h |
| Morphine | 1–7 h |
| Oxycodone | 3–5 h |
| Phenobarbital | 81–117 h |
| Propranolol | 2–6 h |
| Streptomycin | 5–6 h |
| Tetracycline | 7–11 h |
| Valproic Acid | 9–16 h |
| Warfarin | 20–60 h |
FAQs
What's the half-life of Adderall?
The half-life of Adderall is between 9 to 14 hours. It means that after 14 hours, half of the amount you've taken will be already gone from your body.
What drug has the shortest half-life?
Adrenaline (epinephrine) has one of the shortest half-lives at only 2–3 minutes. Adrenaline is a life-saving medication used in severe allergic reactions; due to its short half-life, its dose sometimes has to be repeated.
What drug has the longest half-life?
Amiodarone has one of the longest half-lives — it can take up to 107 days for your body to eliminate just half of a dose. Amiodarone is used to treat certain heart arrhythmias and in resuscitation.
How much Adderall will be in my bloodstream after 6 hours?
Assuming Adderall's half-life is 12 hours and you took 1 g:
- Divide the time by the half-life: 6 / 12 = 0.5
- Raise 0.5 to that power: 0.50.5 = 0.707
- Multiply by the initial dose: 1 g × 0.707 = 0.71 g
After 6 hours, approximately 0.71 g of Adderall remains in your bloodstream.