Does lithium affect Nexplanon (etonogestrel)?

No Clinically Significant Drug Interaction Between Lithium and Nexplanon

Lithium does not affect the contraceptive efficacy or safety of Nexplanon (etonogestrel implant), and no dose adjustments or special monitoring are required when these medications are used together.

Mechanism and Pharmacology

• Nexplanon works through continuous release of etonogestrel, a progestin that inhibits ovulation by preventing the mid-cycle LH surge and maintains serum levels of approximately 200 pg/ml at steady state 1
• Lithium is primarily renally excreted and does not undergo significant hepatic metabolism that would interact with progestin-based contraceptives 2
• Etonogestrel metabolism occurs independently of lithium's pharmacokinetic pathways, with no documented enzyme induction or inhibition interactions 1

Evidence Base

The available evidence shows:

• No documented drug-drug interactions exist between lithium and etonogestrel-containing contraceptive devices in clinical practice 3, 4
• Large-scale safety studies of Nexplanon involving over 7,000 insertions and 5,000 removals did not identify lithium as a contraindication or interacting medication 5
• Lithium's primary concern with NSAIDs (not hormonal contraceptives) relates to reduced renal clearance and increased lithium toxicity risk 2

Clinical Management Algorithm

For patients on lithium requiring Nexplanon:

1. Insert Nexplanon using standard technique - no modifications needed for lithium users 4
2. Continue lithium at current dose - no adjustment required 2
3. Monitor lithium levels per standard protocol (typically every 3-6 months) - Nexplanon does not alter lithium pharmacokinetics 2
4. Counsel on Nexplanon's 3-year duration and >99% contraceptive efficacy regardless of lithium use 6, 7

Important Caveats

• If the patient is on lithium for bipolar disorder, ensure psychiatric stability is maintained, as pregnancy itself (not the contraceptive) poses risks that require careful planning 2
• NSAIDs should be avoided in lithium users due to risk of lithium toxicity, but this is unrelated to Nexplanon 2
• Standard Nexplanon contraindications apply (active thrombosis, liver tumors, undiagnosed vaginal bleeding, breast cancer) regardless of lithium use 3

Monitoring Recommendations

• No additional monitoring beyond routine care is needed for the lithium-Nexplanon combination 5
• Standard lithium monitoring continues: serum levels, renal function (GFR), and thyroid function per established protocols 2
• Nexplanon requires no routine monitoring after insertion, though patients should be counseled on bleeding pattern changes 3, 4