Efficacy, suitability, side-effects, and drug interactions

The pregnancy rate associated with use of an implant is very low < 1 in 1000 over 3 years. Most pregnancies
have occurred when the client was already pregnant prior to insertion of the implant or had not observed
contraceptive cover after initial fitting.

No increased risk of pregnancy has been demonstrated in women weighing up to 149kg. However because of
the inverse relationship between weight and serum etonogestrel levels a reduction in the duration of
contraceptive efficacy cannot be completely excluded. Women using the contraceptive implant should be
informed that earlier replacement can be considered in obese women (but there is no direct evidence to support earlier replacement).

Assessment of client suitability

A medical history (including sexual history) and a clinical assessment, together with consideration of the recommendations in the UK Medical Eligibility Criteria for Contraceptive Use (UKMEC) , should be used to assess the use of the implant.

Assessment of method suitability for the client

• Discuss efficacy and failure rate and provide written method information.
• Fully explain procedure and show demonstration of implant.
• Decision to proceed taken by client and clinician.
• All clients should be counselled and given the opportunity to take time to consider all their contraceptive options, and possible side effects, including changes to bleeding patterns, before implant insertion.
• Further appointment made by client for insertion if required.
• Women using anticoagulants- see FSRH guidance

• Bleeding: Altered bleeding patterns are common among women using an implant. Women should be
  advised that 20% of users will have no bleeding, 33% will have infrequent bleeding, 38% will have
  regular bleeds and 25% have frequent or prolonged bleeding. Women should be advised altered
  bleeding patterns are likely to remain irregular.
• Weight change, mood change, loss of libido: Women should be advised that there is no evidence of a causal association between use of the implant these symptoms.
• Acne: Women should be advised that acne may improve, occur, or worsen during the use of an implant.
• Headache: There is no evidence of causal association between use of an implant and headache.
• Migraine: Women who develop new symptoms of migraine with aura whilst using an implant should be advised to seek medical advice to discuss risks/benefits.
• Breast cancer: There may be an association between current or recent use of hormonal contraception
  (including progestogen-only implants) and a small increase in risk of breast cancer; absolute
  risk remains very small.

It is recommended that you check the current status of drug interaction of new preparations with FSRH CEU Guidance: Drug Interactions with Hormonal Contraception (May 2022), BNF and, if necessary, any interaction with HIV drugs.

Concomitant use of enzyme inducing drugs reduces the efficacy of the implant. Women should be advised to switch to a method unaffected by enzyme inducing drugs or to use additional contraception until 28 days after stopping treatment.