The Mercilon pill offers effective protection against unplanned pregnancy

  • Combined contraceptive pill, using both oestrogen and progesterone

  • Over 99% effective when used correctly

  • Available from £16.95 + Prescription Fees and Delivery Costs

Our prices

Strength Quantity Price Stock
20mcg/150mcg63 tablets£16.95In Stock
Prices exclude a prescription fee. This treatment requires a quick online consultation,
which a doctor will review to determine if a prescription is appropriate.

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Dr Samantha Miller

Reviewed by Dr Samantha Miller MB ChB
(2017, University of Glasgow)
GMC number: 7561464

Information last reviewed 04/03/2021


Mercilon Summary


One pill, taken once er day at the same time each day

Type of Medicine

Hormonal contraceptive


Prevents ovulation, thickens mucus to make it harder for sperm to reach eggs, and prevents egg attachment to the uterus

Available Size

63 tablets

Available Strengths


Active Ingredient



From 27p per pill

Side Effects

Can include breast pain or tenderness, weight increase, mood changes, nausea, vomiting, stomach cramps, low sex drive, fluid retention

What is Mercilon?

Mercilon is a type of combined contraceptive pill, one of the most popular and convenient methods of contraception in the UK. Containing oestrogen and progestogen hormones, the pill is over 99% effective at preventing unplanned pregnancies if used correctly.

How does Mercilon work?

Mercilon contains ethinylestradiol and desogestrel which are synthetic versions of oestrogen and progesterone, the female sex hormones. Taking the pill stops the ovaries from releasing an egg each month. It also causes the mucus surrounding the entrance to the womb to thicken so that sperm cannot enter as easily, and reduces the thickness of the womb lining so that a fertilised egg cannot attach itself. Mercilon essentially causes you to have an artificial menstrual cycle that prevents pregnancy.

How effective is Mercilon?

If Mercilon is taken as instructed it is more than 99% effective. This means not missing pills, taking any late, or having your protection affected by other medications or illness. These are common factors that cause the pill to become less effective, and in fact, with typical use, the pill is around 91% effective at preventing pregnancy. This means that on average, nine women in every one hundred will become pregnant during the first year of pill use.

When does Mercilon start to work?

If you start taking Mercilon on the first day of your period you will be protected from pregnancy right away. Starting Mercilon after the first day of your cycle means that you will need to use condoms, or an alternative barrier method of contraception for the first seven days until the pill starts to work. If you are switching from a different type of combined pill, you should start Mercilon right after finishing the pack of your current pill. You won’t need any additional precautions. If you’re switching from a progestogen-only pill, you can switch at any time, however, you’ll need to use condoms to prevent pregnancy for the first week of pill-taking.

Other uses of Mercilon

Mercilon can also provide relief for women with heavy, painful or irregular periods. An advantage of the combined pill is that it often gives relief from premenstrual syndrome (PMS), and reduces the amount of menstrual blood loss. It can also be used to delay your period once you’ve been taking it for at least three weeks. 


Which ingredients can cause an allergic reaction?

An allergic reaction to Mercilon birth control occurs in less than 1 in 1000 people. Keep an eye out for symptoms of a severe allergic reaction: facial/throat swelling, hives, dizziness, and trouble breathing. Seek emergency medical attention immediately if you notice these symptoms.

Active ingredients

The active ingredients in Mercilon are 20 micrograms of ethinylestradiol (an oestrogen) and 150 micrograms of desogestrel (a progestogen).

Inactive ingredients

The other ingredients are dl-alpha-tocopherol, potato starch, povidone, stearic acid, aerosol and lactose.


What should I do if I missed a pill?

If you miss a pill, do not panic, take a moment to read over the advice leaflet provided in your pill pack. If it has been more than 12 hours since you were due to take it then it's considered a missed pill. Take your missed pill as soon as you're able to, even if that means you are taking two at once. For the next seven days use additional contraception, such as condoms, to protect yourself from pregnancy and keep taking your pills as usual. If you’re in the last seven days of the pack, omit the usual pill-free interval and go right on with the next pack. 

If you have had unprotected sex during this time then you may need emergency contraception which is available from your GP, local pharmacist or sexual health clinic. If you are unsure about what to do then don't hesitate to get advice.

What should I do if I took a pill too late?

If you have taken your pill later than scheduled this is not necessarily something to worry about. As long as you take it within 12 hours of the usual scheduled time, then you will still be protected against pregnancy. Make sure you take the rest of your pills on time. If you’re struggling to remember to take your pill, it might be useful to set an alarm or reminder on your mobile phone. 

How to start Mercilon

The best time to start Mercilon is on the first day of your natural period as you'll then be protected from pregnancy right away. You can also start Mercilon at another time in your cycle, if you can be sure you are not pregnant, however, you will need to use additional precautions for 7 days. If you are switching from another combined contraceptive pill, you should finish your current pack and start taking Mercilon the next day, you probably will not experience a bleed until you come to the end of your first Mercilon pack. If you are switching from a mini-pill (progestogen-only pill), you can start Mercilon at any time, but should use barrier contraception for 7 days.

How to take Mercilon

You should take Mercilon at the same time each day. It's taken every day for 3 weeks and then you have a pill-free week which is when you have a bleed, like a period. The pill strips will usually have the days of the week printed on them to help you remember to take one each day (not including the pill-free week). 

Side Effects

Mercilon side effects

Taking the combined pill increases your risk of having a blood clot. While rare, it's important to be aware of this and look out for any indications or changes while you are on the pill. Your doctor will monitor your blood pressure to make sure it doesn't rise. 

Common side effects associated with Mercilon include: 

  • Changes in bleeding pattern e.g. breakthrough bleeding or spotting
  • Headaches
  • Mood changes including depressed mood
  • Nausea
  • Stomach cramps
  • Breast pain or tenderness
  • Weight increase

These side effects often subside within a couple of months of pill-use. 

Less common side effects may include: 

  • Migraines 
  • Low sex drive
  • Fluid retention 
  • Diarrhoea
  • Vomiting 
  • Breast enlargement
  • Rash, sometimes itchy

Rare side effects may include: 

  • Blood clots in the arteries or veins
  • Hypersensitivity reactions 
  • Changes in vaginal discharge
  • Nipple secretion 
  • Eye discomfort when wearing contact lenses 
  • Erythema nodosum (a skin condition causing raised bumps or lumps)
  • Erythema multiforme (a skin condition causing a red, often circular, rash)
  • Weight loss
  • Increased sex drive 

Mercilon may also increase your risk of:

  • Breast cancer
  • Cervical cancer
  • Liver problems 
  • High blood pressure
  • Gallstones
  • Chorea (jerky, involuntary movements)
  • Stomach problems 
  • Worsening of systemic lupus erythematosus (SLE – an immune condition)
  • Worsening of otosclerosis (a hearing problem)
  • Low or high blood sugar
  • Worsening of porphyria


Mercilon is not suitable for women who: 

  • Have or have ever had a venous thromboembolism (e.g. deep vein thrombosis (DVT) or pulmonary embolism)
  • Have or have ever had an arterial embolism (e.g. myocardial infarction or stroke) or prodromal condition (e.g. angina pectoris or transient ischaemic attack)
  • Have a condition that affects blood clotting e.g. Factor V Leiden, antithrombin-III-deficiency, protein C deficiency and protein S deficiency
  • Have hyperhomocysteinaemia
  • Are known to have antiphospholipid-antibodies, anticardiolipin-antibodies, or lupus anticoagulant
  • Have a history of migraine with neurological symptoms (aura)
  • Have risk factors for blood clots (e.g. severe diabetes, severe hypertension, severe cholesterol problems)
  • Have a known or suspected oestrogen-dependent malignancy e.g. breast cancer
  • Are off their feet for long periods of time
  • Are due to have major surgery with prolonged immobilisation 
  • Have severe liver problems including liver tumours
  • Have unexplained vaginal bleeding 
  • Have pancreatitis
  • May be pregnant
  • Have endometrial hyperplasia
  • Are allergic to any of the ingredients
  • Are over the age of 35 and a smoker

Drug interactions

The following medications interfere with the way Mercilon works: 

  • HIV treatments 
  • Epilepsy treatments
  • Hepatitis C treatments 
  • Rifampicin 
  • Medication for infectious diseases 
  • Medication to treat high blood pressure in the lungs
  • St John's wort

Be sure to tell your prescriber of any regular medications you take. 

Mercilon and alcohol

It's fine to drink alcohol while on Mercilon. There is no known interaction between the two.

Please note: if you vomit within 3-4 hours of taking Mercilon, it may not have been absorbed properly by your body. If this happens, you may need to take another pill as soon as the vomiting stops and then continue taking the rest of your pack as normal. 

Treatment Options

Switching contraceptive pill

Switching contraceptive pill is usually a straightforward process. In most cases, you can stop taking your current pill and start Mercilon right away. If you are on a progestogen-only pill then you can switch at any time, but you will be required to use additional protection e.g. condoms for seven days. Check with your doctor or pharmacist for instructions as it may vary depending on the type of pill you are on.

Mercilon vs the mini pill

The mini pill is also known as the progestogen-only pill (POP). It differs from combined pills such as Mercilon as it only contains a progestogen hormone. This makes it suitable for women who are sensitive to oestrogen or who cannot take the combined pill for medical reasons. The mini pill has fewer associated side effects. 

Alternatives to Mercilon

Gedarel contains exactly the same hormonal components as Mercillon and is available in the same 20mcg/150mcg strength, or a higher 30mcg/150mcg strength. Other commonly prescribed brands of the combined pill are Microgynon, Cilest and Marvelon. Other long term types of contraception are available such as the implant, injection and coil. Visit your GP or family planning clinic to discuss your options for these methods.


Can you use Mercilon for period delay?

You can use Mercilon to delay your period by running two packs of pills together. Usually, you'll take the pill every day for three weeks before having a seven-day break. This is when you will have a bleed. If you skip the pill-free week and start the next pack straight away, you won't have a period until the end of the second pack.

If I have vomited, will Mercilon still work?

Vomiting within three to four hours of taking Mercilon may mean that your body has not been able to absorb the hormones contained in the pill. In this case, take another pill as soon as the vomiting stops and keep taking the rest of your pack as scheduled. Your cycle will be a day shorter than usual. If you continue to vomit then you should use condoms until you have felt better for seven days to ensure you are protected against pregnancy.

When can I get pregnant after taking Mercilon?

You can get pregnant anytime after stopping Mercilon. If you are not planning to start a family right away then it's advisable that you use another method of contraception, like condoms or a diaphragm, until you are ready. When you come off the pill, it usually takes a month or two for your menstrual cycle to return to normal, so for some women, it may take several months to get pregnant. it's different for everybody so it's important not to put too much pressure on yourself and your body.

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