How Does Evra Work in the Body
Chemical Composition, Mechanism of Action & Metabolic Effects Explained
Key Takeaways: How Evra Works
- Active Ingredients: Norelgestromin (progestogen) and ethinyl estradiol (oestrogen) delivered continuously through skin.
- Primary Actions: Inhibition of ovulation, thickening of cervical mucus, and endometrial alteration.
- Release Rate: 203 mcg norelgestromin + 33.9 mcg ethinyl estradiol per 24 hours.
- Metabolism: Liver via CYP3A4 and conjugation; metabolites excreted in urine and faeces.
- Duration: Each patch worn for 7 days; three patches per cycle followed by a patch‑free week.
Evra is a combined hormonal contraceptive patch that releases norelgestromin and ethinyl estradiol through the skin. It prevents pregnancy by suppressing ovulation, altering cervical mucus, and changing the endometrial lining.
Important Medical Advice
Combined hormonal contraceptives like Evra increase the risk of venous and arterial blood clots. Seek immediate medical help if you experience: sudden leg swelling/pain, unexplained breathlessness, chest pain, severe headache, or visual disturbances. See full symptom list in section "Blood clots".
Chemical Composition & Molecular Structure
Each 20 cm² Evra patch contains 6 mg norelgestromin and 600 micrograms ethinyl estradiol. The active substances are embedded in an adhesive matrix that releases them continuously over 7 days.
Structural Details
13‑ethyl‑17‑hydroxy‑18,19‑dinor‑17α‑pregn‑4‑en‑20‑yn‑3‑one oxime
A progestogen derived from norgestrel. It is the active metabolite of norgestimate and acts as a potent progesterone receptor agonist.
19‑nor‑17α‑pregna‑1,3,5(10)‑trien‑20‑yne‑3,17‑diol
A synthetic oestrogen with high oral bioavailability; the ethinyl group at C17 slows hepatic metabolism, allowing transdermal delivery.
Key Pharmaceutical Properties
| Property | Norelgestromin | Ethinyl Estradiol |
|---|---|---|
| Lipophilicity (logP) | 3.8 | 3.67 |
| Protein binding | >97% (albumin, SHBG) | 98% (albumin) |
| Daily release (mcg/24h) | 203 | 33.9 |
| Half‑life (elimination) | ~28 hours | ~17 hours |
🗒️ Pharmaceutical insight: The adhesive matrix contains polyisobutylene/polybutene, crospovidone, and lauryl lactate to ensure consistent drug delivery and skin adhesion.
Mechanism of Action: Dual Hormonal Pathway
Evra prevents pregnancy through three complementary mechanisms typical of combined hormonal contraceptives.
- Ovulation inhibition: The combination suppresses hypothalamic‑pituitary‑ovarian axis, reducing gonadotropin (FSH, LH) secretion and preventing follicular development and ovulation.
- Cervical mucus thickening: Norelgestromin increases mucus viscosity, creating a barrier to sperm penetration.
- Endometrial alteration: The hormones induce a thin, atrophic endometrium that is less receptive to implantation.
| Component | Primary Role | Onset of Action |
|---|---|---|
| Norelgestromin | Progestogenic effects (cervical mucus, endometrial suppression) | 24‑48 hours |
| Ethinyl estradiol | Stabilises endometrium, enhances progestogen activity | Immediate (receptor binding) |
🗒️ Physiological insight: Continuous transdermal delivery avoids peaks and troughs, maintaining stable hormone levels throughout the 7‑day wear period.
Absorption & Distribution (Pharmacokinetics)
After application to clean, dry skin, norelgestromin and ethinyl estradiol diffuse through the stratum corneum and enter the systemic circulation. Steady state is reached within 2 weeks of cyclic use.
Absorption kinetics
Peak serum concentrations occur approximately 48‑72 hours after application. The patch delivers 203 mcg norelgestromin and 33.9 mcg ethinyl estradiol per 24 hours consistently.
Distribution
Both hormones are highly protein‑bound. Norelgestromin binds to albumin and SHBG; ethinyl estradiol binds primarily to albumin. Volume of distribution is ~3‑4 L/kg.
Adhesion studies show that Evra remains effective during daily activities, bathing, and exercise. If a patch detaches for less than 24 hours, it can be reapplied; if longer, a new cycle must be started with backup contraception.
Metabolic Effects & Elimination
Norelgestromin is rapidly metabolised in the liver to norgestrel (active) and various hydroxylated and conjugated metabolites. The main pathway involves reduction and glucuronidation. Excretion is via urine (60%) and faeces (40%).
Ethinyl estradiol undergoes extensive first‑pass metabolism when swallowed, but transdermal delivery bypasses the gut. It is hydroxylated by CYP3A4 to 2‑hydroxy ethinyl estradiol, then methylated or conjugated. About 40% is excreted in urine, 60% in faeces.
⚠️ Metabolic caution: Drugs that induce CYP3A4 (e.g., rifampicin, carbamazepine, St John's wort) may reduce contraceptive efficacy. Use additional barrier methods during and 28 days after such therapy.
Clinical Efficacy & Cycle Control
Pearl Index (pregnancies per 100 woman‑years) for Evra is approximately 0.9 in perfect use and 5.8 in typical use, comparable to combined oral contraceptives. Cycle control is generally good, though breakthrough bleeding and spotting are most common in the first 1‑3 cycles.
Women weighing 90 kg or more may have a higher risk of contraceptive failure; consider alternative methods if BMI ≥ 30 kg/m².
Evra Patch FAQs
How long does Evra take to become effective?
If applied on the first day of your period, Evra is effective immediately. If applied later, use additional contraception (e.g., condoms) for the first 7 days.
Can Evra cause weight gain?
Weight gain is reported as a common side effect (≥1/100), but studies show average changes are modest. Fluid retention may contribute.
What should I do if my Evra patch falls off?
If off for less than 24 hours, reapply or use a new patch immediately – no backup needed. If off longer, start a new 4‑week cycle and use non‑hormonal contraception for the first week.
Does Evra protect against sexually transmitted infections?
No, Evra does not protect against HIV or other STIs. Always use condoms to reduce the risk of STIs.
Can I use Evra while breastfeeding?
No, Evra is not recommended during breastfeeding because oestrogen may reduce milk production and pass into breast milk. Discuss progestogen‑only options with your doctor.
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Medical Content Manager
Nabeel is a co-founder, and medical content manager of Chemist Doctor. He works closely with our medical team to ensure the information is accurate and up-to-date.
Medical Doctor
Dr. Feroz is a GMC-registered doctor and a medical reviewer at Chemist Doctor. He oversees acute condition and urgent care guidance.
Medical Director
Usman is a co-founder, and medical director of Chemist Doctor. He leads the organisation's strategic vision, bridging clinical and operational priorities.
Review Date: 15 March 2026
Next Review: 15 September 2026
Published on: 15 March 2026
Last Updated: 15 March 2026