Yes, it is safe to start lamotrigine while on a birth control implant
Starting lamotrigine (Lamictal) in a patient using an etonogestrel contraceptive implant is safe and does not require any special precautions or dose adjustments. Unlike combined hormonal contraceptives (pills, patches, rings containing estrogen), the progestin-only implant does not interact with lamotrigine in either direction 1.
Key Evidence Supporting Safety
The U.S. Medical Eligibility Criteria for Contraceptive Use explicitly addresses this interaction and assigns it a Category 1 rating (no restriction for use) for lamotrigine with progestin-only contraceptives including implants 1. The guideline states: "No drug interactions have been reported among epileptic women taking lamotrigine and using POCs [progestin-only contraceptives]" 1.
This stands in stark contrast to combined oral contraceptives (COCs) containing estrogen, which receive a Category 3 rating with lamotrigine due to significant bidirectional interactions 1.
Why the Implant is Different
The critical distinction lies in the mechanism of interaction:
- Estrogen-containing contraceptives (pills, patches, vaginal rings) induce hepatic glucuronidation, which significantly increases lamotrigine clearance and can reduce lamotrigine levels by 50-60% 1, 2, 3, 4
- Progestin-only methods like the etonogestrel implant do not induce these metabolic pathways and therefore do not affect lamotrigine concentrations 1, 5
Conversely, lamotrigine does not reduce the effectiveness of progestin-only contraceptives, whereas it can decrease levels of combined oral contraceptives 1.
Clinical Implications
For your patient:
- Start lamotrigine at standard dosing without adjustment for the implant
- No additional contraceptive backup is needed
- The implant will maintain full contraceptive efficacy
- Lamotrigine levels will remain stable throughout the month (no cyclic fluctuations as seen with COCs)
- No increased seizure risk or breakthrough bleeding expected from this combination
Important Caveat About Combined Hormonal Contraceptives
If this patient were considering switching from the implant to a combined hormonal method (pill, patch, or ring) in the future, this would require significant lamotrigine dose adjustments and careful monitoring 1, 6. The FDA label for lamotrigine specifically warns about this interaction and notes that "dosage adjustments will be necessary in most patients who start or stop estrogen-containing oral contraceptives while taking LAMICTAL" 6.
The 2014 AAP guideline on contraception for adolescents notes that "COCs decrease the effectiveness of some medications (e.g., lamotrigine)" 7, but this concern does not apply to progestin-only implants.
Bottom Line
The etonogestrel implant is actually one of the preferred contraceptive options for women taking lamotrigine because it avoids the complex bidirectional pharmacokinetic interactions seen with estrogen-containing methods while providing highly effective, long-acting contraception 8, 9.