Sex Differences in Drug Testing: Why Women Are Underrepresented in Clinical Trials and How Change Is Happening

The podcast examines how drug development has historically centered on male bodies, leading to different safety and efficacy profiles for women. It highlights the underrepresentation of women in clinical trials, the role of historical events like the thalidomide scandal, and ongoing efforts to fix the gap through better data analysis and accountability mechanisms.

• Sex differences influence pharmacokinetics and drug responses across absorption, distribution, metabolism, and excretion.
• Women have often been excluded from trials or had their data not stratified by sex, masking important safety and efficacy differences.
• Real-world examples include ADHD medications, sleep aids like Zolpidem, and cardiovascular drugs with sex-specific dosing gaps.
• Policy responses and industry accountability, such as the Good Pharma Scorecard, are driving global improvements, with examples from India and Africa illustrating broader progress.

Introduction and scope

The podcast, part of a six episode series Women Not Included, explores how medicines are often not designed with women in mind, leading to different outcomes for women and for human health in general. It connects personal experiences with large scale evidence about representation in clinical trials and the pharmacokinetic factors that shape drug action in bodies that differ by sex and gender. The discussion includes insights from Chavi Sachdev in Mumbai and Jennifer Miller from Yale, who coordinates the Good Pharma Scorecard to monitor and expose gender gaps in pharmaceutical research and regulation.

Historical roots and the drive for reform

The conversation situates current gaps within a history of gender bias in medical research. The thalidomide tragedy is described as a tipping point that led to caution around including women of childbearing potential in early research. By the 1990s, policy efforts began to push for better representation, but the actual enforcement was limited; most guidelines remained guidance rather than rules with teeth. The result is a persistent issue: for many years, drugs were tested primarily in healthy young white males, and even when women were included, the data were not routinely analyzed by sex. The podcast notes that about 30% of new drugs lack adequate testing in women, and even when women are included, sex-specific analyses are often missing, leaving clinicians without targeted safety or dosing information for half the population.

Mechanisms of sex differences in pharmacology

Dr Alison McGregor explains the pharmacokinetic framework—ADME: absorption, distribution, metabolism, excretion. She emphasizes that biological sex affects every step. For absorption, differences in gastric pH and gastric emptying can alter how quickly a drug enters the bloodstream. In distribution, women typically have higher body fat and lower total body water, which changes how drugs disperse. Cycle-related fluctuations in estrogen influence liver enzymes that metabolize drugs, and immune system differences rooted in sex chromosomes can shape responses to vaccines and infections. The discussion includes concrete examples such as propofol, where fat storage can affect anesthesia recovery, and ACE inhibitors where kidney function modulates drug clearance and adverse effects. The panel also notes that a higher baseline immune reactivity in women can lead to stronger vaccine responses but also higher adverse drug reactions in some cases.

Case studies and patient-centered implications

The episode highlights 86 drugs with sex-differentiated safety profiles identified in a 2020 study, including aspirin and several migraine and cardiovascular medications. It discusses how migraines have been a predominantly female problem with historically underfunded drug development. ADHD medications like lisdexamfetamine show differing tolerability and efficacy across sexes, potentially due to estrogen–dopamine interactions. Zolpidem, a common sleep aid, required a US FDA dosage adjustment for women after reports of impaired driving, underscoring how sex-specific effects can emerge post-market and drive regulatory change. The discussion makes clear that the lack of initial sex-specific dosing has real-life consequences for patients, including pregnant women who may be treated with off-label prescriptions.

Policy, accountability and global perspectives

Jennifer Miller describes the Good Pharma Scorecard, an index rating pharmaceutical companies on their bioethics performance, including whether pivotal trial demographics match the patient population with the condition. The Scorecard has prompted real changes, with notable improvements after amendment windows and an increasing emphasis on reporting and analyzing data by sex. The podcast highlights global reach: trials are increasingly multinational, and while the US often sets the standards, other countries such as India and regions like Africa are making strides in policy and representation. India enacted guidelines in 2019 prohibiting unwarranted gender discrimination, though not mandating a specific representation ratio. Africa’s HIV cure trial in KwaZulu Natal, all-women participation, is presented as an encouraging sign that gender-focused strategies can address heavy disease burdens in high-risk communities.

Takeaways and call to action

The host and guests emphasize that medicines should be built for all bodies. While there are signs of progress through scorecards and international policy, the field still lacks sex-disaggregated data in many trials, limited sex-specific dosing guidelines for most drugs, and unequal representation across races and geographies. The Good Pharma Scorecard offers a practical way to track improvements and hold sponsors accountable, while broader involvement from health systems, clinicians, and researchers is necessary to ensure that women and pregnant women receive evidence-based care. The podcast ends with an optimistic note about ongoing efforts and the potential for more equitable pharmacology across the globe.

Key takeaways

• Biological sex influences every stage of drug processing and response.
• Historical bias toward male-centric trials persists, though reforms are increasingly underway.
• Data disaggregation by sex is essential to understanding drug safety and efficacy for women.
• Global initiatives like the Good Pharma Scorecard and country-specific guidelines are driving accountability and change.