Contergan is a sedative that was marketed from 1957 to 1961 by the company Chemie Grünenthal. Animal experiments conducted before going to market had not given any indication that the active substance in Contergan - thalidomide - had any undesired side-effects.

Yet it emerged that taking Contergan during pregnancy influenced embryonic development (teratogenic effect). Numerous children whose mothers had taken Contergan during pregnancy suffered deformities of the limbs (dysmelia syndrome).

The Contergan disaster triggered a tightening up of the German Pharmaceutical Products Act (Arzneimittelgesetz). Following the adoption of an amended Pharmaceutical Products Act in 1978 more extensive drug safety checks have been required by law in Germany.

Since animal experiments failed to identify the teratogenic effect of thalidomide, opponents of animal experimentation sometimes cite the Contergan disaster as an illustration of the unreliability of safety tests conducted on animals. The fact is, however, that the harmful effect of Contergan was not discovered in animal experimentation because at that time no experiments had been performed on pregnant animals.

Nevertheless, even subsequent tests on pregnant animals failed to produce a conclusive result: mice and rats proved to be resistant to the teratogenic effect of thalidomide, while in various other animal species - such as rabbits, hamsters, guinea-pigs, dogs and primates - developmental disorders only occurred in some cases.