Benefits, side effects & risks
Benefits
POI may reduce dysmenorrhea and ovulatory pain in some women. There is also some weak evidence that they may help with endometriosis.
Risks
From the available evidence there is little or no increased risk of VTE, stroke or MI with POIm. There is insufficient evidence to state whether it has an adverse effect on BMD at present. As with all progestogen-only contraception, POIm may increase the incidence of breast cancer. Any increased risk though is likely to be small and diminish with time after cessation.
Like many other hormonal contraception, POIm efficacy is potentially reduced in women taking enzyme-inducing drugs.
There is no increased risk of pregnancy with women weighing up to 149kg and, despite ENG levels falling with time, there is no evidence to support replacing POIm earlier than 3 years in these women. There is insufficient evidence in women heavier than 149kg.
Side effects
Unscheduled bleeding is common with POIm and, unlike the other contraceptive methods, it is unlikely to significantly change over time. Studies show only a quarter of women will continue to have regular bleeds. The others may experience amenorrhea (a fifth), infrequent bleeding (a third), or prolonged/frequent bleeding (a quarter). It is a common reason for implant removal.
Other reported side effects include headaches, acne (reports of worsening and improvements), mood change, decreased libido and weight gain, though there is no strong evidence of causal relationship with any of them.
There are reports of skin atrophy and altered sensation around the site of the implant.