There was insufficient evidence from the comparative studies included in these systematic reviews to suggest that one type of subdermal implant was any more or less effective in preventing pregnancy than another, that implants were any more or less effective than the other methods with which they were compared, or that the LNG-20 IUS was any more or less effective than IUDs > 250 mm3. LNG-20 IUS users were significantly less likely to experience either intrauterine or extrauterine pregnancies than were IUD <3 users. Women using the LNG-20 IUS were more likely to experience amenorrhoea, and this event was a notable reason for discontinuation of IUSs.