Does Lamictal Reduce The Effectiveness Of Plan B?

In our latest question and answer, the pharmacist discusses whether or not Lamictal (lamotrigine) reduces the effect of Plan B.

Question

Will lamictal reduce the effect of Plan B? No problem if the Plan B reduces Lamictal results, but i'm wondering if Lamictal will cause an interaction with Plan B to make the emergency contraceptive not work.

Asked by Emilia On Jan 28, 2018

Answered by
Medical Content Reviewed By PharmacistAnswers Staff

On Jan 29, 2018

Lamictal (lamotrigine) is well known to interact with oral hormonal birth control pills. Not only does Lamictal reduce the effectiveness of birth control pills, the overall effect of Lamicital is decreased as well when co-administrated with birth control pills. This is sometimes known as a "bi-directional" interaction.


Plan B (levonorgestrol), is an emergency contraceptive that contains a high dose of the progestin levonorgestrel, which is a commonly used progestin in many birth control pill products. Like regular use birth control pills, Lamictal also interacts with the emergency contraceptive Plan B and reduces its effectiveness.


Plan B - Lamictal (Lamotrigine) Interaction

As we have evidence that Lamictal reduces the efficacy of regular use oral birth control pills, we would rightly assume that it also interacts with emergency hormonal birth control pills as well and multiple studies have confirmed this. As mentioned above, the interaction is "bi-directional", meaning both drugs are affected by this interaction.


Firstly, the estrogen in birth control pills induce (i.e. increase) metabolism of Lamictal (lamotrigine), which results in deceased concentrations of the drug, increasing the risk of breakthrough seizures in individuals. 


Secondly, Lamictal can decrease concentrations of the circulating hormones from birth control by more than 50%, potentially causing failure of contraception and unintended pregnancy. 


It is recommended that anyone taking Lamictal (or other interacting drugs) to see their doctor if they have a need to use emergency contraception. There is no single recommend way to proceed in this situation but there are recommendations including:

  • Insertion of the copper-containing intrauterine device ParaGard. It may be inserted intravaginally up to 120 hours after unprotected sex or within 5 days of expected ovulation to successfully defend against pregnancy.
  • Take a double dose of Plan B or other levonorgestrel emergency birth control pill. For example, some sources recommend to take two doses of Plan B One Step for a total dosage of 3-mg levonorgestrel within 120 hours of unprotected sex.


You and your doctor should determine the best back-up emergency contraception method for your particular situation. 

About the Pharmacist

Dr. Brian Staiger Pharm.D

Dr. Brian Staiger is a licensed pharmacist in New York State and the founder of PharmacistAnswers.com. He graduated from the University At Buffalo with a Doctor of Pharmacy degree in 2010. He has been featured in numerous publications including the Huffington Post as well as a variety of health and pharmacy-related blogs. Please feel free to reach out to him directly if you have any inquiries or want to connect! He's answered thousands of medication and pharmacy-related questions and he's ready to answer yours! Brian.Staiger@PharmacistAnswers.com Office: 716-389-3076

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