Introduction to Transdermal Contraception
The contraceptive patch, known by brand names like Evra, Xulane, and Twirla, is a form of combined hormonal contraception [1.2.5, 1.2.6]. It's a small, thin, beige-colored adhesive square that you stick on your skin [1.2.4]. Once applied, it releases a steady dose of hormones into your bloodstream through the skin to prevent pregnancy [1.2.6]. This transdermal delivery method makes it a convenient option for those who prefer not to take a daily pill, as the patch is only changed once a week [1.5.3]. It works on a four-week cycle: you wear a new patch each week for three consecutive weeks, followed by a one-week patch-free interval where you will typically have a withdrawal bleed, similar to a period [1.4.4].
How Does the Evra Patch Work? The Hormonal Mechanism
The Evra patch contains two synthetic hormones: an estrogen (ethinyl estradiol) and a progestin (norelgestromin) [1.2.1, 1.2.4]. These hormones are similar to the ones naturally produced by the body and are also found in many combination birth control pills [1.2.7]. The patch's effectiveness relies on a three-pronged mechanism of action to prevent pregnancy [1.2.4, 1.5.2].
Preventing Ovulation
The primary way the patch works is by inhibiting ovulation [1.2.1]. The consistent release of estrogen and progestin suppresses the gonadotropins—follicle-stimulating hormone (FSH) and luteinizing hormone (LH)—that are necessary for an egg to mature and be released from the ovary each month [1.5.2]. If no egg is released, fertilization by sperm cannot occur [1.2.4].
Thickening Cervical Mucus
As a secondary mechanism, the hormones in the patch cause the mucus on the cervix to thicken [1.2.3, 1.2.4]. This thicker, stickier mucus acts as a barrier, making it difficult for sperm to swim through the cervix and enter the uterus to reach any potential egg [1.2.6]. It essentially creates a hostile environment for sperm mobility [1.2.1].
Thinning the Uterine Lining
Finally, the hormones also cause the lining of the uterus (the endometrium) to become thinner [1.2.4]. In the unlikely event that ovulation does occur and an egg is fertilized, this thinned lining makes it much less likely for the fertilized egg to successfully implant and develop [1.2.4].
Proper Usage and Schedule
To ensure maximum effectiveness, the patch must be used correctly. It's worn for three weeks in a row, followed by a seven-day patch-free week [1.4.4].
- Application: Apply the patch to clean, dry skin on the buttock, abdomen, upper outer arm, or upper torso (but never on the breasts) [1.4.1, 1.4.3]. Avoid areas with irritated skin, lotions, or creams [1.4.1].
- Schedule: Change the patch once a week, on the same day each week (your "Patch Change Day") for three weeks [1.4.4]. For example, if you apply your first patch on a Sunday, you will change it every Sunday.
- Patch-Free Week: After three weeks (21 days), you remove the patch and do not wear one for seven days (week four) [1.4.4]. You will likely get your period during this week.
- Starting a New Cycle: After the seven patch-free days are over, you apply a new patch on your designated "Patch Change Day" to begin a new cycle, even if you are still bleeding [1.3.6].
If a patch falls off for less than 24-48 hours (depending on the brand), you can usually re-apply it or put on a new one immediately without needing backup contraception [1.8.2]. If it has been off for longer, you should apply a new patch, start a new four-week cycle, and use a backup method like condoms for the first week [1.8.2].
Comparison with Other Contraceptive Methods
The patch offers a different user experience compared to other hormonal methods. Its weekly schedule can be more convenient for some than a daily pill [1.5.3].
| Method | How It's Used | Hormones | Typical Use Effectiveness | Key User Action |
|---|---|---|---|---|
| Evra Patch | Applied to skin weekly for 3 weeks, 1 week off | Estrogen & Progestin [1.2.4] | ~91-93% [1.3.1, 1.3.4] | Remember weekly change |
| Combination Pill | Taken orally every day | Estrogen & Progestin [1.5.5] | ~91-93% [1.5.4, 1.7.3] | Remember daily pill |
| IUD (Hormonal) | Inserted into the uterus by a provider | Progestin-only | >99% [1.7.3] | Provider insertion; check strings |
| Depo-Provera Shot | Injection by a provider every 3 months | Progestin-only | ~94% | Schedule quarterly appointment |
Potential Risks and Side Effects
Like all combined hormonal contraceptives, the patch has potential side effects. Common ones include skin irritation at the application site, breast tenderness, headaches, and nausea, which often subside after the first few months [1.6.5].
A significant consideration is the risk of venous thromboembolism (VTE), or blood clots. Studies have shown that patch users may be exposed to about 60% more estrogen than those on a typical birth control pill, which could increase the risk of blood clots [1.2.1, 1.5.2]. This risk is higher for individuals who smoke (especially those over 35), are overweight (patch may be less effective in women weighing 198 lbs/90 kg or more), or have a history of blood clots, heart attack, stroke, or certain cancers [1.6.1, 1.6.2]. For this reason, a full medical history should be discussed with a healthcare provider before starting the patch [1.6.4]. The patch does not protect against sexually transmitted infections (STIs) [1.2.3].
Conclusion
So, how does the Evra patch work? It functions as a highly effective hormonal contraceptive by delivering a continuous dose of estrogen and progestin through the skin. This hormonal combination primarily prevents pregnancy by stopping ovulation and is supported by secondary actions that block sperm and prevent implantation. Its weekly application offers convenience, but it is not without risks. The increased estrogen exposure and associated risk of blood clots, along with specific contraindications, mean it is crucial to consult with a healthcare professional to determine if the contraceptive patch is a safe and suitable option for your individual health profile and lifestyle.
For more detailed information, consult a healthcare provider or visit a reputable source like Planned Parenthood.
