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expert reaction to study investigating the effects of the pregnancy test hormone Primodos on zebrafish embryos

A new study, published in Scientific Reports, examines the effects of a pregnancy test hormone’s components on the embryos of zebrafish.


Statement on the impact of the study on currently available medicines

Dr June Raine, Director of Vigilance and Risk Management of Medicines, MHRA, said:

“Patient safety is our highest priority and the safety and effectiveness of all available medicines is kept under constant review. As new data comes to light, action is taken as appropriate to make sure the benefits of medications outweigh the risks.”


Statement on the impact of the study on the Report of the Expert Working Group of the Commission on Human Medicines

Dr June Raine, Director of Vigilance and Risk Management of Medicines, MHRA, said:

“The Expert Working Group of the Commission on Human Medicines conducted a comprehensive independent scientific review of all available evidence including this then-unpublished scientific study and their overall conclusion was that the available scientific evidence, taking all aspects into consideration, did not support a causal association between the use of Hormone Pregnancy Tests such as Primodos during early pregnancy and birth defects or miscarriage.

“The Expert Working Group made a number of future-facing recommendations and our focus is now on implementing these.

“While the review cannot take away from the very real suffering experienced by the families involved, it helps shape the path to further strengthen the scientific evidence which supports safety monitoring of medicines in pregnancy.”


Prof. Stephen Evans, Professor of Pharmacoepidemiology, London School of Hygiene and Tropical Medicine (LHSTM), said:

“A key question is whether these results have relevance in the human situation. Giving two tablets over two days in the use for pregnancy testing does not correspond to the dosing regime used for the zebrafish in this study, and replicating the transient changes that would be seen in human usage is difficult.

“The study does not address the separate effects of norethisterone acetate (NA) and ethinylestradiol (EE) contrasted with their combination. From a toxicological standpoint, this would seem to be a weakness.

“There are good human data that show that combined oral contraceptives given in pregnancy do not have the adverse effects suggested. The quotation of some human studies that found some defects with hormonal pregnancy tests is highly selective, and the studies that failed to reproduce the quoted studies have been ignored.

“These observations are interesting but require much more work and replication by other groups, (especially on the effects of NA and EE separately) before they can be regarded as changing the current picture for human use.”


* ‘The Primodos components Norethisterone acetate and Ethinyl estradiol induce developmental abnormalities in zebrafish embryos’ by Brown et al. will be published in Scientific Reports on Tuesday 13 February.


Declared interests

Dr June Raine: “No conflicts of interest”

Prof. Stephen Evans: “I was (am) a member of the Expert Working Group that concluded there was insufficient evidence of a causal effect of Primodos on birth defects.”

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