The precise mechanism of action for thalidomide was not known until the twenty-first century, although efforts to identify thalidomide's teratogenic action generated more than 2,000 research papers and the proposal of 15 or 16 plausible mechanisms by 2000. The primary mechanism of action of thalidomide and its analogs in both their anti-cancer and teratogenic effects is now known to be as cereblon E3 ligase modulators.
Thalidomide also binds to and acts as an antagonist of the androgen receptor and hence is a nonsteroidal antiandrogen of some capacity. In accordance, it can produce gynecomastia and sexual dysfunction as side effects in men.