In the 1950s, scientists did not know that the effects of a drug could be passed through the placental barrier and harm a foetus in the womb, so the use of medications during pregnancy was not strictly controlled. And in the case of thalidomide, no tests were done involving pregnant women.

As the drug was traded under so many different names in 49 countries, it took five years for the connection between thalidomide taken by pregnant women and the impact on their children to be made. A UK Government warning was not issued until May 1962.



One reason why researchers and doctors were slow to make this connection was due to the wide range of changes to foetal development. Limbs, internal organs including the brain, eyesight and hearing could all be affected.

Later, they found that the impact on development was linked to when during pregnancy the drug was taken, and effects only occurred between 20 and 37 days after conception. After that, thalidomide had no effect on the foetus.

Another reason why it took so long to establish the link to thalidomide was that some of the damage caused by the drug was very similar to certain genetic conditions that affect the upper or lower limbs.