Mercilon Tablets

There is a question many women have asked their GP or pharmacist at some point: if my pill is working but I keep getting headaches or feeling sick in the first few weeks, is there a lower-dose option that still does the job? For women already on a desogestrel-based combined pill, the clinical answer is often yes.

Mercilon contains ethinylestradiol 20 micrograms and desogestrel 150 micrograms. It is manufactured by Organon Pharma UK Limited and is licensed in the United Kingdom for the prevention of pregnancy. The 20 microgram oestrogen dose places Mercilon at the lower end of the oestrogen range used in combined oral contraceptives. Its sister preparation Marvelon contains the same desogestrel component at the same dose, but with 30 micrograms of oestrogen instead. Switching between the two is sometimes used clinically to address tolerability issues while keeping the same progestogen. Gedarel 20/150 is the generic equivalent of Mercilon.

One clinical point is worth being clear about from the outset: a lower oestrogen dose does not reduce the VTE risk profile associated with desogestrel. That risk is primarily driven by the progestogen, not the oestrogen dose. If you are switching to Mercilon for VTE-related reasons rather than tolerability reasons, the prescriber will need to discuss this carefully with you.

Mercilon is a monophasic film-coated combined oral contraceptive tablet. Each tablet contains:

1. Ethinylestradiol 20 micrograms: a synthetic oestrogen
2. Desogestrel 150 micrograms: a synthetic third-generation progestogen

Monophasic means every active tablet in the 21-tablet pack delivers an identical hormone dose. There is no step change in dose across the pack. You take one tablet daily for 21 days, then pause for seven days before starting the next pack.

Mercilon and Marvelon sit in the same desogestrel-based combined pill family, distinguished only by oestrogen dose. Gedarel 20/150 (Gedeon Richter) is clinically equivalent to Mercilon; Gedarel 30/150 is clinically equivalent to Marvelon. All four are considered interchangeable within their respective oestrogen dose pairs under NHS and FSRH prescribing guidance. The table below illustrates how they relate:

1. Mercilon (Organon): ethinylestradiol 20 mcg + desogestrel 150 mcg – branded originator
2. Gedarel 20/150 (Gedeon Richter): ethinylestradiol 20 mcg + desogestrel 150 mcg – generic equivalent of Mercilon
3. Marvelon (Organon): ethinylestradiol 30 mcg + desogestrel 150 mcg – same progestogen, higher oestrogen dose
4. Gedarel 30/150 (Gedeon Richter): ethinylestradiol 30 mcg + desogestrel 150 mcg – generic equivalent of Marvelon

Ovulation Suppression

Ethinylestradiol and desogestrel together suppress the pituitary hormones that drive ovulation. Follicle-stimulating hormone and luteinising hormone are both inhibited. Without the luteinising hormone surge, the ovary does not release an egg. This is the primary contraceptive mechanism and is identical to that of Marvelon and all other combined pills.

Cervical and Endometrial Effects

1. Desogestrel thickens the cervical mucus, creating a barrier that is less permeable to sperm.
2. The hormonal environment alters the endometrial lining, reducing its readiness for implantation.

What the Lower Oestrogen Dose Actually Changes

Reducing oestrogen from 30 mcg to 20 mcg does not change the primary contraceptive mechanism. Ovulation is still suppressed, and the secondary effects on cervical mucus and the endometrium remain active. What the dose reduction may affect is tolerability. Oestrogen-related side effects such as nausea, breast fullness, and fluid retention are dose-dependent to some extent in some women. A reduction may reduce these effects, or it may not: individual variability is significant and cannot be predicted from dose alone.

The 21-Day Withdrawal Cycle

After 21 days of active tablets, the seven-day break allows hormone levels to drop. This produces a withdrawal bleed that is typically lighter and shorter than a natural period. The bleed is a hormonal consequence of the break, not evidence of a true menstrual cycle. Starting a new pack more than seven days after the previous pack ends risks a gap long enough for ovarian follicle development to begin.

When to Start

1. Day 1 start: Begin on the first day of your period. Protection is immediate.
2. Days 2 to 5 start: Begin within the first five days of your cycle. Use a barrier method for the first seven days.
3. Switching from Marvelon or another combined pill: Take the first Mercilon tablet the day after your last active tablet from the previous pack. No gap is needed and protection continues without interruption.
4. Switching from a progestogen-only pill: Start on any day. Use barrier contraception for the first seven days.

Daily Use

One tablet daily at the same time for 21 consecutive days. After the 21st tablet, pause for exactly seven days. Restart the next pack on day 29. The break must not go beyond seven days.

1. Swallow each tablet whole with water.
2. Taking tablets at the same time each day maintains consistent blood levels.
3. Vomiting within two hours of taking a tablet, or severe diarrhoea, may prevent full absorption. Treat situation as a missed pill.

Missed Pill Protocol

1. Under 24 hours late: take the missed tablet immediately and continue the pack at the usual time. You remain protected.
2. Over 24 hours late: take the missed tablet now and take the next at the usual time, even if that means two tablets in one day. Use a barrier method for the next seven days.
3. Two or more missed tablets: take only the most recently missed tablet, discard the others, continue the pack, and use barrier contraception for seven days. If the missed tablets fell in week one and unprotected sex occurred during that window, contact a prescriber or pharmacist about emergency contraception.

For vomiting, diarrhoea, or scenarios not covered above, the Patient Information Leaflet contains a complete missed dose guide, or your pharmacist can advise directly.

Tablet Composition

1. Ethinylestradiol 20 micrograms per tablet
2. Desogestrel 150 micrograms per tablet
3. 21 active tablets per pack; no inactive placebo tablets
4. Monophasic: every tablet contains an identical dose

Dosage Regimen

One tablet daily at the same time for 21 consecutive days, followed by a seven-day tablet-free interval. The dose is fixed. There is no escalation, titration, or variation across the pack. Your prescriber confirms the appropriate starting day based on your individual circumstances.

Side effect information below is based on the current UK SmPC for Mercilon. Not every woman will experience side effects. Read the full Patient Information Leaflet before starting treatment.

Common Side Effects

• Headache
• Nausea, especially in the first few weeks
• Breast tenderness or discomfort
• Mood changes, including low mood or mood swings
• Reduced libido
• Irregular spotting or altered bleeding pattern in the first one to three cycles
• Changes in vaginal discharge

Less Common Side Effects

• Weight changes
• Contact lens intolerance caused by changes in corneal curvature
• Chloasma: patchy skin darkening, most commonly on the face, aggravated by sun exposure

Serious Side Effects: Seek Urgent Medical Attention Immediately If You Notice

• Sudden chest pain, breathlessness, or coughing blood: possible pulmonary embolism or heart attack.
• Pain, swelling, redness, or warmth in one leg: possible deep vein thrombosis.
• Sudden severe headache, loss of vision, facial drooping, slurred speech, or weakness on one side: possible stroke.
• Acute severe abdominal pain: possible liver events or ectopic pregnancy.
• Yellowing of the skin or eyes: possible hepatic dysfunction.

The VTE Risk: Oestrogen Dose Does Not Change the Progestogen Category

All combined oral contraceptives raise VTE risk above the baseline for women using no hormonal contraception. Desogestrel-containing pills including Mercilon sit in a higher VTE risk category than levonorgestrel-containing pills. This is the MHRA's confirmed position and applies to both Mercilon (20 mcg) and Marvelon (30 mcg). Reducing the oestrogen dose from 30 to 20 mcg does not reclassify Mercilon into a lower-risk group. A prescriber assessing VTE suitability will treat Mercilon and Marvelon as equivalent in risk class. Your personal risk factors, including BMI, smoking history, family history of clotting, and planned immobility, will all form part of that assessment.

Medicines That Reduce Mercilon's Effectiveness

Enzyme-inducing medicines speed up the breakdown of ethinylestradiol and desogestrel, reducing contraceptive reliability:

• Rifampicin and rifabutin
• Antiepileptic medicines including phenytoin, carbamazepine, phenobarbital, primidone, and topiramate
• HIV antiretrovirals including ritonavir and efavirenz
• St John's Wort, sold without prescription in health food stores and pharmacies

Declare all medicines and supplements at every consultation. If an enzyme-inducing medicine is added while you are taking Mercilon, your prescriber will advise whether additional contraception is needed or a different method is more appropriate.

Mercilon Is Not Suitable If You:

• Have ever had a deep vein thrombosis, pulmonary embolism, stroke, or heart attack
• Experience migraine with aura: the stroke risk associated with oestrogen and aura applies at 20 mcg as it does at any oestrogen dose
• Have uncontrolled hypertension
• Have active or past liver disease, liver tumours, or jaundice caused by previous contraceptive use
• Have a current or previous diagnosis of breast cancer or another oestrogen-sensitive malignancy
• Are pregnant or think you may be pregnant
• Are breastfeeding a baby under six weeks of age
• Smoke and are aged 35 or older
• Have diabetes with established vascular disease

Mercilon May Be Appropriate If You:

• Are a healthy adult woman with no contraindications to combined hormonal contraception
• Have experienced persistent oestrogen-related side effects such as nausea, headache, or breast tenderness on Marvelon or another 30 mcg combined pill, and your prescriber considers a dose reduction to 20 mcg clinically reasonable
• Are already stable on Mercilon or Gedarel 20/150 and need a continuation prescription
• Are switching from a different 20 mcg combined pill and your prescriber is reviewing the progestogen component

Discuss With Your Prescriber Before Starting If You:

• Smoke and are under 35. Smoking compounds cardiovascular risk with all oestrogen-containing contraceptives at every age.
• Have a BMI above 30. Obesity raises VTE risk independently of the pill.
• Have a first-degree relative who developed a clot before age 50. This suggests a possible inherited clotting tendency that warrants further investigation before a desogestrel pill is prescribed.
• Experience migraine without aura. Prescribing requires individual clinical review of migraine frequency, severity, and pattern.
• Are planning long-haul travel or face extended immobility in the near term. Both independently elevate clot risk.

Pharmacy Planet is a GPhC registered UK online pharmacy. Prescriptions for Mercilon are only issued following a clinical consultation reviewed by a registered prescriber. The process is as follows:

You complete a detailed medical questionnaire. The questions about VTE risk, migraine history, blood pressure, family history of clotting, and current medicines are not optional fields. They form the clinical basis for the prescriber's assessment of whether desogestrel at 20 mcg oestrogen is safe and appropriate for you. The specific detail that makes Mercilon distinct from higher-dose alternatives, that lower oestrogen does not reduce the desogestrel VTE risk classification, is something your prescriber will factor into their decision.

A registered prescriber reads your completed questionnaire and makes a clinical judgement. The possible outcomes include: a prescription for Mercilon, a recommendation for a different preparation, a request for clarifying information, or a referral for an in-person assessment. Completing the questionnaire does not determine the outcome. The prescriber does.

Repeat supply consultations follow the same structure. Your health circumstances are reviewed at each request. There is no automated renewal.

• Store below 25°C. Keep the pack away from radiators, windowsills, and direct sunlight.
• Leave tablets in the original foil blister until the moment you take them. The foil protects from moisture and helps you track daily use.
• Keep Mercilon out of reach and sight of children at all times.
• Do not use tablets after the expiry date printed on the carton and blister.
• Return unused or out-of-date tablets to any pharmacy. UK pharmacies accept returned medicines for safe disposal under Duty of Care regulations at no charge.

This reference guide compares the contraceptive preparations available at Pharmacy Planet, grouped by delivery method and formulation type. Every preparation is a Prescription Only Medicine. A registered prescriber will review your individual health profile, contraceptive history, and risk factors before recommending any preparation. This table is a clinical reference, not a recommendation.

Combined Oral Contraceptive Tablets (Monophasic)

Monophasic combined pills contain the same dose of both hormones in every active tablet. The table below compares commonly prescribed monophasic combined oral contraceptives by progestogen type, oestrogen dose, VTE risk category, pack format, and key clinical characteristics.

Important: This comparison is for general information only and does not replace medical advice. A prescriber will decide which treatment is suitable for you following an online consultation.

Mercilon is prescribed when a prescriber has made an active clinical decision: that a 20 mcg oestrogen dose with desogestrel is more appropriate for a specific patient than the alternatives. That decision involves weighing the tolerability advantage of a lower oestrogen dose against the desogestrel VTE risk profile, against your personal medical history. It is not a decision that can be made accurately by an algorithm or a simple online tick-box form.

At Pharmacy Planet, every consultation is read and assessed by a registered prescriber who takes clinical responsibility for the outcome. We do not issue prescriptions by volume. If the clinical picture does not support Mercilon, the prescriber will say so and explain what would be more appropriate. We treat that as a function of good pharmacy practice, not a failure of the service.

Our GPhC registration and the Internet Pharmacy logo appear on our website and can be verified independently at www.pharmacyregulation.org. Our pharmacy team is available at every stage of the consultation and after dispensing if questions arise.

• Organon Pharma UK Limited. Mercilon film-coated tablets – Summary of Product Characteristics. Available at: www.medicines.org.uk/emc/product/1360. Accessed May 2026.
• Faculty of Sexual and Reproductive Healthcare (FSRH). Combined Hormonal Contraception – Clinical Guidance. Available at: www.fsrh.org. Accessed May 2026.
• NHS. Combined pill – your contraception guide. Available at: www.nhs.uk/conditions/contraception/combined-contraceptive-pill. Accessed May 2026.
• British National Formulary (BNF). Ethinylestradiol with desogestrel. Available at: bnf.nice.org.uk. Accessed May 2026.
• MHRA. Combined hormonal contraceptives and venous thromboembolism – updated guidance. Available at: www.gov.uk/government/organisations/medicines-and-healthcare-products-regulatory-agency. Accessed May 2026.