The available experience indicates that, in general, drugs interfering with contraceptive efficacy of Mona Lisa IUDs are highly unlikely. However, published reports appear to show diminished efficacy in the presence of long-term use of non-steroidal anti-inflammatory drugs (especially acetylsalicylic acid) and corticoids. Short-term use in the treatment of dysmenorrhoea with not-steroidal anti-inflammatory drugs does not appear to reduce contraceptive efficacy.