Women experience almost twice as many side effects from medications as men. The reason is not that women are more sensitive. The reason is that most medications were developed based on male biology, dosed for male bodies, and prescribed to women without the necessary data. Here's how this happened and why it still matters today.
For over two decades, millions of women in the US and Europe took the wrong dose of Ambien every night.
The US Food and Drug Administration (FDA) approved zolpidem, the active ingredient in Ambien, in 1992. It was primarily tested on men. It was dosed for men. And it was prescribed to women at the same dose without anyone investigating how the female body metabolizes it. Because that investigation never took place.
Women metabolize zolpidem 50% slower than men. The same dose that was largely metabolized in men by morning still circulated in dangerous concentrations in women's blood when they got behind the wheel.
It took twenty-one years and an archive of court records of women charged with DUI and violent crimes who had no memory of the incidents, all while on a correctly prescribed sleeping pill at a dose their bodies couldn't metabolize, until the FDA halved the recommended dose for women in 2013.
Following the change, reported side effects in women decreased by 38%. This 38% represents twenty-one years of avoidable harm.
Ambien is not an isolated case. It is merely the example that became too public to ignore. The same gap exists for antidepressants, cardiovascular medications, antipsychotics, pain relievers, anticoagulants, and dozens of other drug classes that women take daily in dosages designed for a different body.
Why the female body processes medication differently
The differences in drug metabolism between men and women are not subtle.
Women generally have lower activity in important liver enzymes, especially CYP3A4. This enzyme metabolizes a significant portion of currently approved medications. Lower enzyme activity means active ingredients are broken down more slowly, remain in the body longer, and reach higher peak concentrations than the same dose in a man.
In addition, women have a higher proportion of body fat, different kidney excretion, a different gastric emptying rate, and hormonal fluctuations throughout the cycle that can change drug metabolism by up to 30% depending on the cycle phase.
The birth control pill can reduce the effectiveness of epilepsy medications by 50 to 60%. Women would therefore need to adjust their dose throughout their cycle, without ever being told that this interaction exists.
These are not fringe cases or rare sensitivities. These are documented physiological characteristics of the female body that the pharmaceutical industry systematically disregarded when medications were predominantly developed in male subjects.
A study in Biology of Sex Differences found a sex-specific dosing gap for at least 86 FDA-approved medications. These included aspirin, morphine, heparin, and antidepressants such as sertraline and bupropion. Women metabolized almost all of them slower than men. In 96% of cases, this led to significantly higher rates of side effects in women.
The medications were the same. The body was different. Research never accounted for this difference.
The extent of the side effect problem
According to FDA data, women experience side effects 80 to 90% more often than men. Some analyses suggest almost double.
In the US, women account for around 59% of all redeemed prescriptions. They are therefore the primary users of the drug system and are harmed by it significantly more often than the group for which it was developed.
This is not a rare special case. This is the normal experience of taking medications as a female patient that were developed, tested, and dosed for someone else.
Digoxin, a heart medication prescribed to millions of people, produces 20 to 30% higher blood concentrations in women at the standard dose. This increases the risk of poisoning by 40% and leads to nausea, confusion, and dangerous heart arrhythmias.
Antidepressants from the SSRI group cause nausea and dizziness 1.5 to 2 times more often in women than in men. Antipsychotics such as haloperidol carry a 2.3 times higher risk of dangerous heart arrhythmias in women.
These are not theoretical risks from small studies. They are documented, published, and in most cases known for years before the dosage was adjusted. If it was adjusted at all.
It's not just Ambien – that's just the tip of the iceberg. There are sex-related differences in many medications. Some of these are well-known; others are barely noticed.
— Dr. Janine Clayton
How exclusion from research created the dosing problem
The dosing problem is a direct consequence of exclusion from research.
In 1977, the FDA recommended excluding women of childbearing age from early phases of drug trials. The intention was to protect unborn children from experimental drugs after the thalidomide scandal.
The result was that for sixteen years, the pharmacokinetic data that determines dosing—how quickly an active ingredient is absorbed, how it is distributed in the body, how it is metabolized, and how it is excreted—was collected almost exclusively from male subjects.
When women were finally included in studies after the NIH Revitalization Act of 1993, the dosages were already established. And the tacit assumption that male data could be applied to female bodies was already ingrained in clinical guidelines, prescribing habits, and package inserts, which in many cases were never reviewed.
Even where women have been included in studies since 1993, sex-disaggregated analysis is not consistently mandated. That is, the practice of analyzing the results of male and female participants separately to identify differences.
Including women in a study is not the same as investigating how women respond. A study can have 40% female participants and still only report overall results that obscure sex-specific differences in efficacy, side effects, and optimal dosing.
This gap between inclusion and analysis means that even the approval process after 1993 has yielded incomplete data on female physiology for many approved medications.
When Dr. Mary Claire Haver, Dr. Vonda Wright, Dr. Stacy Sims, and Dr. Natalie Crawford appeared on The Diary of a CEO in October 2025, they spoke directly about the practical consequences of this research failure in clinical practice.
Crawford described patients who were prescribed medications at standard doses and experienced side effects that were dismissed as anxiety, hypochondria, or personal sensitivity, rather than as a pharmacological reaction of a body for which the medication was never designed.
Wright described how the clinical guidelines she was trained on were based on research that systematically underrepresented precisely those patients she actually treats.
Sims, whose work specifically addresses how female and male physiology differ in response to nutrition, training, and active ingredients, has documented for years the practical consequences of the assumption that male data can be directly applied to women. They cannot. The difference between male and female physiology is real, measurable, and consequential.
What this means beyond prescription medications
The same logic applies to dietary supplements. The industry is less regulated than the pharmaceutical industry. So the requirement to include women in testing and to evaluate results by sex is even less consistently applied here.
Most formulas were developed from research on male subjects, often male athletes, and dosed based on male pharmacokinetics.
The female hormonal cycle changes how the body absorbs, distributes, metabolizes, and reacts to active ingredients throughout the month. A formula created without female-specific research cannot account for this.
The problem is not limited to prescription medications under medical supervision. It affects every protein, every vitamin, every performance supplement, and every longevity active ingredient that women buy, assuming it was developed with their biology in mind. In most cases, it was not.
Developing a product specifically for women requires female subjects in research, endpoints relevant to women in study design, and the intellectual honesty to state what is known and what is not.
The NMN study by Yoshino et al. (2021), the most cited human study on NMN, was conducted exclusively with postmenopausal women and measured outcomes directly relevant to female metabolic health. This is not the norm. It is what it means to take biology seriously. And that it even stands out says more about the low starting point.
The supplement you're taking today was almost certainly developed without a woman in the room. The question is whether the brand you choose has changed that.
Where science stands today
The FDA's 2024 guidance has tightened requirements for diversity in clinical trials and emphasized the need for equitable representation in drug research. The US National Institutes of Health (NIH) now requires biological sex to be considered as a variable in preclinical research. This means animal studies must include female animals and report results by sex before human studies begin.
These changes are significant, and they are long overdue. But they do not retroactively correct decades of approvals based purely on male data. They do not change clinical guidelines that still do not reflect sex-specific dosages. And they do not change the prescribing habits of a medical profession trained on research that treated male biology as a universal standard.
The 2024 report by McKinsey and the World Economic Forum names insufficient science as one of three structural causes of the health gap. It states that only about 10% of clinical trials for ischemic heart disease and migraines report sex-disaggregated data, even though both conditions disproportionately affect women or progress differently in them.
The gap between what is known and what is applied in practice remains substantial in almost every medical field. And the women living in this gap are not abstract political problems. They are women taking incorrect medication dosages, suffering avoidable side effects, and being told their reaction is a personal sensitivity rather than a pharmacological failure.
Ambien was the example that became too public to ignore. For dozens of other medications, the evidence is just as clear and just as old. The research exclusion that created this problem is documented history. The dosing gap that resulted from it is a current reality. And the assumption that male data can be applied to female biology, never scientifically substantiated and practically always harmful, persists to this day in the systems that determine which medications women take and how much of them.
Sources
- Zucker, I., & Prendergast, B. J. (2020). Sex differences in pharmacokinetics predict adverse drug reactions in women. Biology of Sex Differences, 11(1), 32. https://doi.org/10.1186/s13293-020-00308-5
- US Food and Drug Administration. (2013). FDA drug safety communication: Risk of next-morning impairment after use of insomnia drugs containing zolpidem. https://www.fda.gov/drugs/drugsafety/ucm334033.htm
- Association of American Medical Colleges. (2024). Why we know so little about women's health. https://www.aamc.org/news/why-we-know-so-little-about-womens-health
- NIH Office of Research on Women's Health. History of women's participation in clinical research. https://orwh.od.nih.gov/toolkit/recruitment/history
- McKinsey Health Institute & World Economic Forum. (2024). Closing the women's health gap: A $1 trillion opportunity. https://www.mckinsey.com/mhi/our-insights/closing-the-womens-health-gap-a-1-trillion-dollar-opportunity-to-improve-lives-and-economies
- Haver, M. C., Wright, V., Sims, S., & Crawford, N. (2025, 16. Oktober). Hormone & fertility experts: We've been lied to about women's health. The Diary of a CEO with Steven Bartlett.
- Yoshino, M., Yoshino, J., Kayser, B. D., et al. (2021). Nicotinamide mononucleotide increases muscle insulin sensitivity in prediabetic women. Science, 372(6547), 1224–1229. https://doi.org/10.1126/science.abe9985
- Frontiers in Pharmacology. (2023). A systematic review on sex differences in adverse drug reactions related to psychotropic, cardiovascular, and analgesic medications. https://doi.org/10.3389/fphar.2023.1096366