London School of Hygiene & Tropical Medicine

Many experts, including myself, share the recent concerns laid out by the British Pharmacological Society, highlighting the urgent need for clearer guidance on the use of medicines during pregnancy and breastfeeding. I also agree that it’s time to include more women in drug trials, capitalising on the significant advances made in recent years which allow us to do this in a safe and effective way. 

Currently, women are understandably anxious about taking medicines when pregnant or breastfeeding. It’s important to stress that this does not mean medicines used in pregnancy or breastfeeding are unsafe. Many medicines have strong safety records and are used safely every day. The challenge is that for some medicines, the evidence base is thinner than we would ideally like, and improving research will help clinicians and patients make more confident decisions.

The issue is longstanding and historically rooted in reasonable concerns that pregnant and breastfeeding women were better protected by excluding them from trials testing medicines. There is a long history of protection through exclusion, shaped by the thalidomide events of the late 1950s. This created a culture that contributed to distrust among some groups of women toward medical research.

This approach has also left a crucial evidence gap within this population, but significant advances in pre-clinical testing, modelling and real-world evidence now offer opportunities to support the safer inclusion of these populations in drug development.

As many as 90% of pregnant women with a chronic condition take at least one medication, and at least half of breastfeeding women also use medicines. Yet pregnant women were represented in only 1.1% of clinical trials and breastfeeding women in 0.6% of trials submitted to the Medicines and Healthcare products Regulatory Agency (MHRA) between 2019 and 2023. 

There are also practical challenges. Recruitment and retention of pregnant and breastfeeding women can be more difficult due to time constraints, financial burden, and breastfeeding logistics.

At a regulatory level, inclusion should, in principle, be considered for all relevant medicinal products. Pharmaceutical sponsors will likely require either incentives or mandated requirements to ensure inclusion of these populations where appropriate. Pre-clinical testing and pharmacokinetic modelling should begin early in drug development, and may need to be mandated to support the safe inclusion of pregnant and breastfeeding women in trials.

The question should no longer be whether pregnant and breastfeeding women should be included in research, but how their inclusion can be done safely and responsibly. Better evidence on the safety and efficacy of medicines in these populations, including information on appropriate timing and dosing, would lead to better treatment decisions.