Can Zepbound (zepine) lower the effectiveness of Nexplanon (etonogestrel implant)?

Zepbound (Tirzepatide) and Nexplanon (Etonogestrel Implant) Interaction

Based on current evidence, there is no indication that Zepbound (tirzepatide) reduces the effectiveness of Nexplanon (etonogestrel implant).

Mechanism of Action and Potential Interactions

Zepbound (tirzepatide) is a GIP/GLP-1 receptor agonist that works through metabolic pathways, while Nexplanon contains etonogestrel, a progestin that works primarily through hormonal mechanisms. The key considerations for potential interactions include:

Metabolic Pathways

• Nexplanon's effectiveness can be compromised by medications that induce hepatic enzymes in the cytochrome P450 pathway 1
• Known medications that reduce Nexplanon effectiveness include:
  • Certain anticonvulsants (e.g., carbamazepine) 2
  • Some antiretroviral medications (particularly efavirenz) 1, 3

Current Evidence on Zepbound

• No guidelines or research indicate that GLP-1 receptor agonists like tirzepatide affect hormonal contraceptive efficacy
• Tirzepatide does not induce hepatic enzymes in the cytochrome P450 pathway that would affect etonogestrel metabolism

Medications Known to Reduce Nexplanon Effectiveness

For context, medications that are known to reduce Nexplanon effectiveness work through specific mechanisms:

1. Hepatic Enzyme Inducers: Medications that induce cytochrome P450 enzymes can accelerate the metabolism of etonogestrel, potentially reducing contraceptive efficacy 1, 3

2. Documented Interactions:

   • Efavirenz (antiretroviral): Decreases etonogestrel levels 1
   • Carbamazepine (anticonvulsant): Associated with contraceptive failure 2

Nexplanon Efficacy and Considerations

Nexplanon is highly effective with typical use:

• Failure rate of only 0.05% 3
• Provides contraception for up to 3 years 3, 4
• Rapid return to fertility after removal 5

Clinical Recommendations

If a patient is using both Zepbound and Nexplanon:

• No additional contraceptive measures are needed based on current evidence
• Regular follow-up is appropriate as with any contraceptive method
• Monitor for any changes in bleeding patterns, which is the most common side effect of Nexplanon 5

Important Considerations

• If the patient is also taking medications known to affect Nexplanon (such as certain antiretrovirals or anticonvulsants), additional contraceptive methods may be warranted 1, 3
• Weight changes from Zepbound therapy do not appear to affect Nexplanon efficacy, as studies show Nexplanon remains effective even in women weighing ≥70 kg 4
• If there are concerns about potential drug interactions not yet documented in research, using a backup method like condoms would provide additional protection

In conclusion, patients can be reassured that current evidence does not suggest any interaction between Zepbound and Nexplanon that would reduce contraceptive efficacy.