A 4-year pilot study on the efficacy and safety of Implanon, a single-rod hormonal contraceptive implant, in healthy women in Thailand

Eur J Contracept Reprod Health Care. 1998 Jun;3(2):85-91. doi: 10.3109/13625189809051409.


Objective: To investigate the contraceptive efficacy, safety and acceptability of a new single-rod, progestogen-only contraceptive implant (Implanon).

Methods: In an open, non-comparative pilot study, 100 healthy women received a contraceptive implant containing the progestogen etonogestrel (3-ketodesogestrel) for 2 years with an optional extension up to 4 years.

Results: Subjects were exposed to Implanon for 296.1 woman-years. There were no pregnancies during the study. Per 90-day reference period, the median number of bleeding-spotting days was 10 and the median number of bleeding-spotting episodes was 2. Amenorrhea occurred in 24-39% of subject during the first 2 years and in about 20% in those who continued in the 3rd and 4th years. The most common drug-related adverse event was headache (7%). A slight increase in body mass index was observed. Only a few subjects discontinued treatment early, due to bleeding irregularities (6%) or amenorrhea (1%). The cumulative discontinuation rates were 13.4% after 2 years, 25.3% after 3 years and 28.0% after 4 years of use. Within 3 months of implant removal, six normal pregnancies occurred, indicating a rapid return of fertility. The average time taken for insertion of the implant was 0.5 min, compared with 2.5 min for removal.

Conclusions: Implanon demonstrated excellent contraceptive efficacy and was well tolerated during up to 4 years of use. The vaginal bleeding pattern was variable and was characterized by relatively few bleeding events, but proved acceptable to most subjects. Because of its single-rod design, Implanon was quickly inserted and removed without complications.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adult
  • Contraceptive Agents, Female / adverse effects
  • Contraceptive Agents, Female / therapeutic use*
  • Desogestrel*
  • Female
  • Humans
  • Menstrual Cycle / drug effects*
  • Pilot Projects
  • Reference Values
  • Thailand
  • Vinyl Compounds / adverse effects
  • Vinyl Compounds / therapeutic use*


  • Contraceptive Agents, Female
  • Vinyl Compounds
  • etonogestrel
  • Desogestrel