We understand from the passage that when thalidomide was first developed in the late 1950s it looked safe ----.

Thalidomide was unique. In every animal test
used in the late 1950s, it had a clean bill of health.
It was chemically related to other drugs which had
been in use for a long time. Over-dosage with
thalidomide was unlikely to prove fatal. It was
marketed in Europe and in Britain as a "safe
sedative". The tragic results that followed its use
by women in the early weeks of pregnancy are
how well known. Babies were born with severe
deformities of limbs, internal organs or both. That
effect could not have been foretold from any
animal tests in use at that time. Since that date
new drugs have been subjected to strict testing in
various animal species to check the effect on
foetal development, along with the older tests for
toxicity which had always been undertaken by
well-known drug companies.