99+% effective with perfect and typical use; less than one out of every 100 people will become pregnant each year
Additional Sources for Effectiveness Ratings and Use:
The What, the Why, the Where, the When, and the How-to: The currently available contraceptive implant, Implanon, is a thin, plastic rod inserted subdermally (under the skin) by a healthcare provider in the non-dominant arm which emits small amount of the hormone progestin over time. That progestin prevents pregnancy by suppressing ovulation and thickening cervical mucus, making it difficult for sperm to swim to the cervix.
A backup method of birth control should be used after insertion of the implant for two weeks before using the implant alone. One implant is effective for three years, and if a person wants to stop using it, she can just have it removed. For those wishing to become pregnant, once removed, people will resume their normal fertility cycles.
Pros of the implant include not having to think about a method for as long as three years at a time, a very high level of effectiveness, no chance of user error, reduction of painful periods, and a method which doesn't interrupt sexual activities.
The biggest complaint most users have with the implant is due to unpredictable spotting or bleeding which, for some, may be very frequent. Some people may stop getting their periods, and may have very irregular periods; some may have heavier, longer periods than usual. Other unfavorable side effects may include those typical with many hormonal methods like weight gain, vaginal dryness, reduction of sex drive, nausea or an increase in headaches. The implant can pose cardiovascular risks, irritation of the injection site, difficulty in removing the implant, and some people are not good candidates for the implant, possibly including diabetics, those with high blood pressure, those suffering from depression or epilepsy. Some other medications or drugs may reduce the effectiveness of the implant.
For more information about Implanon, see:
When Good Birth Control Does Bad Things: It's highly unlikely that an implant will fail, but if used with a medication that can decrease effectiveness it may fail, and if a person does not get a new implant in time when her old one has expired, pregnancy may occur.
What will/might you need to discuss or negotiate with a partner?
Other methods which can be used as a backup method with an implant: Implants are so effective and free of user error that unless using a medication known or suspected to decrease effectiveness, a backup is not likely needed after the first two weeks post-insertion. But if a backup is needed, it can be used with any non-hormonal method.
Other methods you might like if you like the implant:
Why would an implant be a good option for me? If any of the following are true:
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Don't forget: Statistically, sexually active young adults are as, if not more, likely to acquire a sexually transmitted infection (STI) as you are to become pregnant. Although 15-24-year-olds represent only one-quarter of the sexually active population, they account for nearly half of all new STIs each year, and of the 18.9 million new cases of STIs each year, 9.1 million (48%) occur among 15-24-year-olds (AGI). Often people have some funny ideas about who is most likely to get an STI, but the fact of the matter is that younger people -- of any sexual orientation, any economic class, any kind of relationship -- have been the highest risk group for some time now.
Condoms are the only method of birth control which also provide protection against STIs. It's pretty typical for younger people to ditch condoms if they have another method of birth control, so just remember that STIs are still a risk if you're using another method. You can read all about safer sex here -- Safe, Sound & Sexy: A Safer Sex How-To -- but the rule of thumb most medical experts and prevention organizations suggest, which we also encourage at Scarleteen is six months of safer sex, six months of sexual monogamy, and then TWO full STI screenings for each partner -- once at the start of that six months, once at the end -- before ditching latex barriers.