What is the interaction between hormonal birth control and lamotrigine (anticonvulsant medication)?

Interaction Between Hormonal Birth Control and Lamotrigine

Combined hormonal contraceptives containing estrogen significantly reduce lamotrigine serum concentrations by 40-60%, potentially causing breakthrough seizures, while progestin-only contraceptives do not affect lamotrigine levels. 1

Key Interactions

Effect of Hormonal Contraceptives on Lamotrigine

• Combined hormonal contraceptives (CHCs):

  • Reduce lamotrigine serum concentrations by 40-60% 1
  • Ethinyl estradiol is the component responsible for this interaction 2
  • CDC classifies this as Category 3 (risks generally outweigh benefits) 3
  • Can lead to breakthrough seizures during active hormone weeks 1
  • May cause lamotrigine toxicity during hormone-free weeks when lamotrigine levels rise 1, 4

• Progestin-only contraceptives:

  • No significant effect on lamotrigine levels 2
  • CDC classifies as Category 1 (no restrictions) 3, 1
  • Includes progestin-only pills, DMPA injections, and implants 1

Effect of Lamotrigine on Contraceptive Efficacy

• Lamotrigine does NOT reduce contraceptive efficacy, unlike enzyme-inducing antiepileptic drugs 1
• May slightly decrease levonorgestrel concentrations (by approximately 19%), but this doesn't appear to affect contraceptive efficacy 5

Recommended Contraceptive Options for Women Taking Lamotrigine

First-line options (Category 1):

• Progestin-only methods:
  • Progestin-only pills
  • DMPA injections
  • Implants
  • Levonorgestrel IUD

Not recommended (Category 3):

• Combined hormonal contraceptives containing estrogen:
  • Combined oral contraceptives
  • Contraceptive patch
  • Vaginal ring

Management Recommendations

For women starting lamotrigine who need contraception:

1. Choose progestin-only methods as first-line options
2. Avoid combined hormonal contraceptives containing ethinyl estradiol

For women already on lamotrigine who want to start hormonal contraception:

1. Recommend progestin-only methods as first choice
2. If combined hormonal contraceptives must be used:
   • Measure baseline lamotrigine serum concentrations
   • Monitor for breakthrough seizures
   • Consider increasing lamotrigine dose by 50-100% to maintain therapeutic levels
   • Monitor lamotrigine levels 2-3 weeks after starting contraception

For women using both lamotrigine and combined hormonal contraceptives:

1. Monitor for breakthrough seizures during active hormone weeks
2. Watch for signs of lamotrigine toxicity during hormone-free weeks
3. Consider adjusting lamotrigine dosing throughout the cycle
4. Measure lamotrigine serum concentrations after any regimen change

Important Caveats

• Significant interpatient variability exists in the magnitude of this interaction 4
• Hormone replacement therapy with estrogens may also reduce lamotrigine levels 6
• Standardize blood sampling in relation to contraceptive cycle when monitoring lamotrigine levels 4
• Even with decreased levonorgestrel levels, contraceptive efficacy appears to be maintained 5

By understanding these interactions and following appropriate management strategies, clinicians can help women taking lamotrigine maintain both seizure control and effective contraception.