Frequently Asked Questions

HalfLife is an interactive pharmacokinetics visualization tool that shows how drug concentration changes in the body over time. Using established mathematical models of drug absorption, distribution, and elimination, it generates real-time concentration-time curves for over 30 common medications. HalfLife is designed to make one of pharmacy's core concepts — drug half-life — intuitive and accessible to patients, students, and curious minds alike.

No. HalfLife is strictly an educational tool. The simulations use population-average pharmacokinetic parameters drawn from clinical literature, which means they represent a statistical average — not your individual biology. Factors like your age, kidney function, liver health, genetic makeup, body weight, and other medications you take can significantly alter how a drug behaves in your body. Never use HalfLife to decide whether to take, skip, or stop a medication. Always consult your pharmacist or physician.

HalfLife was built by Jay, a licensed pharmacist and researcher. Jay also develops PK·Swift, a professional pharmacokinetics calculation tool used by pharmacists and clinical researchers. HalfLife is his attempt to bring that same pharmacokinetic rigor to a general audience — making the science visual, accessible, and genuinely educational. It is published under Vibed Lab, a small independent studio building precise and useful digital tools.

Every pharmacokinetic parameter in HalfLife — half-life, volume of distribution, bioavailability, absorption rate — is sourced from peer-reviewed clinical literature, including reference pharmacology textbooks and published drug package inserts. Where ranges are reported in the literature (which is common), the simulator uses the midpoint of the clinically accepted range as its default value. Sources are curated and verified by a licensed pharmacist.

Yes, HalfLife is completely free to use. There are no accounts, no subscriptions, and no paywalls. The site is supported by non-intrusive display advertising. We believe pharmacokinetics education should be accessible to everyone.

Navigate to the Simulator page and select a drug from the dropdown menu. The simulator will immediately display a concentration-time curve using default clinical values for that drug. You can then adjust the dose, dosing interval, number of doses, and route of administration using the controls provided. The chart updates in real time as you make changes.

The current version of HalfLife simulates one drug at a time. Each drug profile includes its own set of pharmacokinetic parameters, and the chart reflects only the selected drug's concentration curve. Multi-drug overlay simulation — useful for studying drug interactions and timing — is a feature being considered for a future release.

The curve plots the estimated concentration of a drug in your bloodstream (vertical axis, in ng/mL or equivalent units) against time elapsed since the first dose (horizontal axis, in hours or days). Peaks represent moments of maximum concentration after each dose (C_max), troughs represent the lowest concentration before the next dose, and the gradual decline between doses illustrates first-order elimination — the mathematical process governed by the drug's half-life.

The simulations are mathematically accurate representations of population-average pharmacokinetic models. They correctly apply first-order elimination kinetics and one-compartment pharmacokinetic principles. However, the accuracy of the output depends entirely on the accuracy of the input parameters — and those parameters are averages, not individual measurements. Real-world drug levels in any given person can differ substantially from what the simulator predicts. The simulations are best understood as illustrative models, not personal forecasts.

Steady state is the condition reached after multiple doses of a drug where the amount of drug entering the body with each dose equals the amount being eliminated between doses. At steady state, peak and trough concentrations stabilize and repeat predictably with each dosing cycle. For most drugs, steady state is achieved after approximately 4–5 half-lives of regular dosing. The simulator visualizes this accumulation process over multiple doses and shows the plateau that defines steady state.

Drug half-life (t½) is the time required for the concentration of a drug in the bloodstream to decrease by 50%. It is one of the most fundamental concepts in pharmacokinetics because it governs how frequently a drug must be taken to maintain therapeutic levels, how long it takes for the drug to reach steady state, and how long it takes the drug to clear the body after the last dose. A drug with a short half-life (like ibuprofen at ~2 hours) requires more frequent dosing than a drug with a long half-life (like fluoxetine at ~2–6 days).

Biological variability is the short answer. Drug half-life is influenced by individual differences in liver enzyme activity, renal function, body composition, age, sex, genetic polymorphisms (such as CYP2D6 metabolizer status), and co-administered medications that inhibit or induce metabolic enzymes. Clinical studies measure half-life in populations of volunteers or patients, and the results naturally span a range. For example, the antidepressant fluoxetine has a reported half-life of 1–4 days for the parent compound, and 4–16 days for its active metabolite norfluoxetine.

Drug elimination rate is determined by several factors. Hepatic (liver) clearance depends on the activity of metabolizing enzymes, particularly the cytochrome P450 family; genetic variation and enzyme-inhibiting drugs can dramatically slow this process. Renal (kidney) clearance depends on glomerular filtration rate, which declines with age and kidney disease. Body composition affects volume of distribution — highly lipophilic drugs distribute widely and eliminate more slowly. Protein binding also matters: only the unbound fraction of a drug is pharmacologically active and available for elimination.

Bioavailability is the fraction of an administered dose that reaches the systemic circulation in an active form. An intravenous dose has 100% bioavailability by definition, since it is delivered directly into the bloodstream. Oral bioavailability is typically lower because drugs must survive the gastrointestinal environment and first-pass metabolism in the liver before reaching systemic circulation. For example, oral morphine has roughly 20–40% bioavailability because the liver heavily metabolizes it before it reaches the blood. Bioavailability directly affects how large an oral dose must be to achieve the same effect as an IV dose.

Food affects drug absorption in several ways. For some drugs, food slows gastric emptying, which delays absorption and reduces peak concentration — a beneficial effect that can prevent gastrointestinal irritation (e.g., ibuprofen, metformin). For other drugs, food increases bioavailability by stimulating bile production or altering gut pH (e.g., griseofulvin, certain antifungals). Conversely, food can reduce absorption for some drugs by binding to them in the gut or changing the absorption environment — which is why some antibiotics and thyroid medications are taken on an empty stomach. Your pharmacist can explain which scenario applies to your specific medications.

No. HalfLife does not collect, store, or transmit any personally identifiable information. There are no accounts, no login, and no cookies set by our application. All simulator inputs exist only in your browser session and are never sent to our servers. Standard server access logs (IP address, browser type, pages visited) are maintained by our hosting provider, Vercel, for infrastructure purposes. See our Privacy Policy for full details.

Yes, and we encourage it. If there is a medication you would like to see in the simulator, you can submit a suggestion via the Contact page or by opening a GitHub issue. Please include the drug name (generic preferred), the indication if known, and any published pharmacokinetic reference you can find. All additions are vetted against peer-reviewed clinical literature before being included.

HalfLife is a progressive web application (PWA) built with Next.js. It is fully optimized for mobile browsers and works well on smartphones and tablets without any installation. You can add it to your home screen from your mobile browser's share menu for an app-like experience. A dedicated native app for iOS and Android is not currently planned, as the web version provides equivalent functionality.