One-Size Dosing and the Patients It Leaves Behind: The 70-Kilogram Standard You've Never Heard Of
A Number That Quietly Shapes Your Prescription
The next time a pharmacist hands you a prescription bottle, consider that the dose printed on that label may have been determined, at least in part, by a reference standard established decades ago: a hypothetical 154-pound (70-kilogram) adult male. This figure, sometimes called the "Reference Man," was embedded into early pharmacokinetic research and regulatory frameworks, and its influence has persisted far longer than most patients—or even many clinicians—realize.
This is not a fringe concern. It is a documented feature of how pharmaceutical science evolved, and its consequences for real patients can range from mildly suboptimal treatment to genuinely dangerous outcomes. For women, older adults, individuals with low body weight, and those with certain metabolic profiles, a "standard" dose may be anything but standard.
How Pharmaceutical Dosing Standards Were Built
When researchers conduct clinical trials to establish a drug's effective dose, they rely on the population enrolled in those trials. For much of the twentieth century, that population skewed heavily toward young, healthy adult males. Women were formally excluded from many early-phase clinical trials until the 1990s, partly due to concerns about fetal exposure to experimental compounds and partly due to assumptions that hormonal variability would complicate data interpretation.
The Food and Drug Administration did not formally require the inclusion of women and minorities in clinical trials until the FDA Modernization Act of 1997, and even after that milestone, underrepresentation remained a persistent issue. The result: dosing recommendations for many medications that have been in use for decades were effectively derived from a narrow demographic slice and then applied universally.
The 70-kilogram figure itself emerged from occupational health research in the mid-twentieth century, where it was used to model radiation exposure and later absorbed into pharmacology as a convenient reference point. It was never intended to represent every patient—it was a mathematical convenience. Yet it became the invisible foundation beneath countless prescribing decisions.
Why Body Composition and Sex Matter More Than You Think
Drug behavior inside the body—how it is absorbed, distributed, metabolized, and eliminated—is profoundly influenced by individual physiology. These processes, collectively described as pharmacokinetics, do not operate uniformly across different bodies.
Body fat distribution affects how drugs are stored and released. Many medications are lipophilic, meaning they dissolve preferentially in fat tissue. Women, on average, carry a higher proportion of body fat relative to lean mass than men of similar weight, which can cause certain drugs to accumulate differently, prolonging their effects or intensifying them.
Kidney and liver function govern how quickly the body clears medications. Both organs tend to decline in functional capacity with age, meaning older adults often process drugs more slowly. A dose calibrated for a 35-year-old man may linger far longer—and at higher concentrations—in a 72-year-old woman.
Enzyme activity varies significantly by sex. The cytochrome P450 enzyme system, which is responsible for metabolizing a large proportion of prescription drugs, includes several enzymes that are expressed differently in men and women. CYP3A4, one of the most clinically relevant of these enzymes, tends to be more active in women, while CYP1A2 activity is generally higher in men. These differences directly affect how quickly certain drugs are broken down and how much active compound reaches the bloodstream.
Real-World Consequences: When the Standard Dose Fails
The case of zolpidem (sold under the brand name Ambien) is among the most cited examples of sex-based dosing failure. For years, zolpidem was prescribed at a standard 10-milligram dose for both men and women. In 2013, the FDA took the unusual step of requiring manufacturers to lower the recommended dose for women to 5 milligrams for immediate-release formulations, after data confirmed that women cleared the drug significantly more slowly than men—leaving many with dangerously impairing blood concentrations the following morning. Reports of women involved in traffic accidents and other impairment-related incidents had accumulated for years before regulatory action followed.
Cardiovascular medications have also drawn scrutiny. Research published in peer-reviewed cardiology literature has documented that women experiencing heart attacks are more likely to receive doses of antiplatelet and anticoagulant therapies that, when calibrated against their lower average body weight and different platelet biology, may contribute to higher rates of bleeding complications compared to male patients receiving the same regimens.
Among older adults, inappropriate dosing is a recognized contributor to adverse drug events, which the Centers for Disease Control and Prevention (CDC) identifies as a significant cause of emergency department visits and hospitalizations in the United States each year. The Beers Criteria, a clinical reference maintained by the American Geriatrics Society, exists specifically because the standard adult dose is frequently inappropriate for patients over 65—yet awareness of this resource among non-specialist prescribers remains uneven.
What Personalized Dosing Actually Looks Like in Practice
The concept of individualized dosing is not new, but its application remains inconsistent. In certain therapeutic areas—oncology, for instance—dosing is routinely calculated based on body surface area or weight, acknowledging that a uniform dose is pharmacologically irrational. Pediatric medicine has long operated on weight-based dosing as a foundational principle. The question is why this logic has not been applied more systematically to adult medicine.
Therapeutic drug monitoring (TDM) is one practical tool that allows clinicians to measure actual drug concentrations in a patient's blood and adjust doses accordingly. It is standard practice for medications with narrow therapeutic windows, such as lithium, warfarin, and certain antibiotics. Expanding its use—or at minimum, applying more individualized dosing calculations at the point of prescribing—could meaningfully reduce the incidence of both under-treatment and toxicity.
Pharmacogenomic testing, which examines how a patient's genetic makeup influences drug metabolism, represents a more advanced layer of personalization. Several major health systems across the United States now offer pharmacogenomic panels that can flag patients as poor, intermediate, normal, or rapid metabolizers for specific enzyme pathways—information that can directly inform dosing decisions before a single pill is swallowed.
How to Advocate for the Right Dose at Your Next Appointment
As a patient, you are not expected to audit the clinical trial history behind every medication you take. However, there are concrete steps you can take to ensure your dose is appropriate for your individual profile.
Share your complete picture. Inform your prescriber of your current weight, any significant changes in weight, your age, and any known kidney or liver conditions. These factors directly influence dosing calculations and are sometimes overlooked in routine appointments.
Ask about sex-specific dosing. If you are a woman being prescribed a medication that has documented pharmacokinetic differences between sexes—ask directly whether the recommended dose accounts for those differences.
Request a medication review if you are over 65. Clinical pharmacists and geriatricians are particularly well-equipped to assess whether your current regimen reflects age-appropriate dosing. Many Medicare Advantage and Part D plans cover medication therapy management (MTM) consultations at no additional cost.
Inquire about pharmacogenomic testing. If you have experienced unexpected side effects or a lack of response to a medication, ask your provider whether genetic testing might explain the discrepancy and guide an alternative dosing strategy.
The Evolving Standard
The pharmaceutical industry and regulatory agencies have made meaningful progress in recent years. The FDA's Drug Trials Snapshots program now publishes demographic data on clinical trial participants for newly approved drugs, increasing transparency around who was—and was not—studied. The agency has also issued guidance encouraging sponsors to analyze trial data by sex, age, and race to identify subgroup differences in efficacy and safety.
But progress in research does not automatically translate to updated prescribing habits for the thousands of medications already on the market. The 70-kilogram man may be a relic of a less rigorous era, but his shadow still falls across the prescribing landscape. Knowing that it exists is the first and most important step toward stepping out of it.
