What is Primodos and why were 100 UK families seeking compensation?

theguardian.com:

The high court in London has struck out a bid by families who believe their babies were harmed to sue the pharmaceutical company behind the hormone-based pregnancy test Primodos. Scientists first published concerns about birth defects in the 1960s, a decade before the tests were withdrawn, but the evidence for a causal link remains contentious.

Primodos was an oral hormonal pregnancy test introduced to the UK in the late 1950s. It involved taking two pills on consecutive days containing norethisterone, a synthetic progesterone, and ethinyl estradiol, an artificial oestrogen. If a woman was not pregnant, the pills would trigger a period, meaning no bleeding indicated pregnancy. The concentration of the hormones was high – one dose of Primodos contained about 40 times the level in modern contraceptive pills.

In 1967, Isabel Gal, a paediatrician at Queen Mary’s hospital for children, in Surrey, published findings suggesting a link between Primodos and birth defects. The study, a survey of 100 mothers whose babies had been born with congenital abnormalities, found that 19 of the women, compared with four in a control group, had used the pregnancy test drug. After concerns were raised, the pharmaceuticals company Schering removed pregnancy testing as one of the uses of Primodos, stating it should only be used to treat irregular periods. The drug was voluntarily withdrawn from the market in 1978 for commercial reasons.

Since Primodos was withdrawn other studies, including a 2018 systematic review by Oxford scientists, have reported a statistically significant association between the tests and congenital abnormalities, including neural tube and heart defects. However, the issue remains contentious. In 2017, the expert working