The contraceptive implant, known by brand names like Nexplanon and formerly Implanon, is a small, flexible rod inserted under the skin of the upper arm [1.3.7]. It releases a progestin hormone called etonogestrel to prevent pregnancy for up to three years [1.2.3, 1.3.7]. While highly effective, its performance can be compromised by certain external factors, primarily other medications and supplements that affect how the body metabolizes this hormone.
How Medications Affect the Implant
Some medications, known as enzyme-inducing drugs, can speed up the breakdown of the etonogestrel hormone in your liver [1.2.3]. This lowers the level of the hormone in your bloodstream, making the implant less effective at preventing pregnancy [1.5.5]. If you are taking a medication known to interact, your healthcare provider may recommend using an additional non-hormonal contraceptive method, such as condoms [1.3.2]. This backup method is often advised for the duration of the treatment and for 28 days after stopping the interacting medication [1.3.2].
Prescription Medications of Concern
It's essential to inform any healthcare provider that you have a contraceptive implant before starting a new medication [1.3.2]. Several classes of prescription drugs have been identified as having significant interactions:
- Anti-seizure Medications (Antiepileptics): Many drugs used to treat epilepsy, migraines, or nerve pain can decrease the implant's effectiveness. These include Carbamazepine, Phenytoin, Phenobarbital, Topiramate, Oxcarbazepine, and Lamotrigine [1.2.7, 1.2.8].
- Tuberculosis (TB) and Antibiotics: While most common antibiotics like amoxicillin do not interfere with the implant, Rifampin (also known as Rifadin) is a notable exception [1.5.4, 1.6.4]. This antibiotic, primarily used for TB, significantly reduces the implant's effectiveness [1.6.6]. Griseofulvin, an antifungal, can also lower efficacy [1.5.5].
- HIV Medications: Certain antiretroviral drugs used to manage HIV, such as Efavirenz, Lopinavir/Ritonavir, and Nevirapine, can interfere with the implant [1.2.8, 1.5.5].
- Pulmonary Hypertension Medication: Bosentan (Tracleer) is known to make the implant less effective [1.3.1, 1.5.3].
- Nausea Medication: Aprepitant, used to prevent nausea and vomiting from chemotherapy, may also decrease how well the implant works [1.3.1, 1.2.5].
- Stimulants: Certain stimulants like modafinil (Provigil) and armodafinil (Nuvigil) can speed up the breakdown of the implant's hormone, reducing its effectiveness [1.5.2].
Herbal Supplements and Other Substances
The most well-documented herbal supplement that interferes with hormonal contraception is St. John's Wort [1.4.2]. Often taken for depression, it is an enzyme inducer that can lower the concentration of contraceptive hormones in the blood, potentially leading to unintended pregnancy [1.4.1, 1.4.4, 1.4.5]. Other supplements like alfalfa and saw palmetto have also been suggested to potentially affect hormone levels, though research is less extensive [1.4.3].
Interestingly, grapefruit and grapefruit juice can also have an effect, but in the opposite direction. They can slow down the breakdown of the hormone, increasing its levels in the body and potentially raising the risk of side effects like headaches or breast pain [1.5.2, 1.5.5].
Comparison of Interfering Substance Types
| Substance Category | Examples | Primary Effect on Implant | Recommended Action |
|---|---|---|---|
| Anti-Seizure Meds | Carbamazepine, Topiramate, Phenytoin [1.2.7] | Decreases effectiveness | Use a backup contraceptive method [1.3.2] |
| Specific Antibiotics | Rifampin, Griseofulvin [1.6.4, 1.5.5] | Decreases effectiveness | Use a backup contraceptive method [1.3.2] |
| HIV Antiretrovirals | Efavirenz, Ritonavir [1.2.8] | Decreases effectiveness | Discuss options with your doctor [1.2.5] |
| Herbal Supplements | St. John's Wort [1.4.2] | Decreases effectiveness | Avoid use; use backup contraception [1.4.1] |
| Other Substances | Grapefruit Juice [1.5.2] | May increase side effects | Monitor for side effects; consult a doctor [1.5.5] |
Do Other Factors Interfere?
Questions often arise about other factors like body weight. Extensive research has shown that the contraceptive implant remains highly effective for overweight and obese individuals, with failure rates not varying significantly by Body Mass Index (BMI) [1.7.1, 1.7.2]. Unlike the contraceptive patch or some emergency contraception pills, the implant's efficacy is not considered to be compromised by weight [1.7.5, 1.7.7].
Incorrect insertion is another potential, though rare, cause of failure [1.3.6]. It is crucial that the implant is inserted correctly by a trained healthcare professional. You should be able to feel the implant in your arm after insertion [1.2.3].
Conclusion
The contraceptive implant is one of the most reliable birth control methods available. However, its effectiveness is not absolute and can be compromised by a specific list of enzyme-inducing medications and supplements. Open communication with all your healthcare providers about your implant and any new medications—prescription, over-the-counter, or herbal—is the most critical step you can take to ensure your implant continues to provide maximum protection against unintended pregnancy. Always consult a healthcare professional before starting or stopping any medication to understand potential interactions.
For more information on drug interactions, you can visit the official Nexplanon website.
