The Mercilon pill offers effective protection against unplanned pregnancy

Mercilon is a combined contraceptive pill, one of the most popular and convenient contraceptive methods in the UK. Mercilon is over 99% effective when used correctly.

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What is Mercilon?

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

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 entrance to the womb to thicken so that sperm cannot enter with ease 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 as ovulation is prevented while you are on the pill. 

How effective is Mercilon?

If Mercilon is taken as instructed it is more than 99% effective. This means not missing pills or having your protection affected by other medications or illness. These are common factors which cause the pill to become ineffective. 

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. If you are swapping to Mercilon from a different type of pill or contraceptive then you can usually start taking it at any time during your cycle without having to wait. Starting Mercilon after the fifth 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.

Other uses of Mercilon

Mercilon can also provide relief for women with heavy, painful and irregular periods. The advantage of the combined pill is that it provides you with control over your period, giving a lighter flow with reduced PMS. 


Active ingredients

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

Inactive ingredients

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


How to start Mercilon

The best time to start Mercilon is on the first day of your period as you'll be protected from pregnancy right away. You can start Mercilon in this way on days 1-5 of your period but if you have a shorter cycle you may not be protected right away by starting on day five. Otherwise, if you begin taking the pill at any other time during your cycle you'll need to use condoms for the first seven days. 

How to take Mercilon

You should take Mercilon at the same time each day. It's taken everyday for 3 weeks and then you have a pill free week which is when you have your period. The pill strips will usually have the days of the week printed on them to help you remember to take it each day. 

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 provided with your pills. If it has been more than 24 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 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 24 hours then you will still be protected against pregnancy. Make sure you take the rest of your pills on time and if you miss any then use condoms for the next seven days as your protection may be affected. 

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: 

  • Headaches
  • Nausea
  • Stomach cramps
  • Depression
  • Mood changes
  • Breast pain or tenderness
  • Breakthrough bleeding or spotting 

These side effects should subside within a couple of months.

Less common side effects may include: 

  • Migraines 
  • Low sex drive
  • Fluid retention 
  • Acne
  • Diarrhea
  • Vomiting 
  • Breast enlargement

Rare side effects may include: 

  • Irregular vaginal bleeding 
  • Nipple secretion 
  • Hypersensitivity 
  • Eye discomfort when wearing contact lenses 
  • Erythema nodosum
  • Erythema multiforme
  • Weight loss
  • Increased sex drive 
  • Breast cancer
  • Cervical cancer
  • Liver problems 
  • High blood pressure
  • Gallstones
  • Chorea (jerky, involuntary movements)
  • Stomach problems 
  • Worsening of systemic lupus erythematosus
  • Worsening of otosclerosis
  • Low or high blood sugar
  • Worsening of porphyria


Mercilon is not suitable for women who: 

  • Have or have ever had a blood clot
  • Have a condition which affects blood clotting
  • Have or have ever had breast cancer
  • Are off their feet for long periods of time
  • Are due to have surgery 
  • Have ever had a stroke or heart attack 
  • Have every had angina pectoris 
  • Have severe diabetes 
  • Have high cholesterol 
  • Have liver problems
  • Have ever experienced a migraine with aura
  • Have unexplained vaginal bleeding 
  • Have pancreatitis
  • May be pregnant
  • Are breastfeeding  

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

Mercilon and alcohol

It's fine to drink alcohol while on Mercilon. There is not interaction between the two. 

Treatment Options

Mercilon vs the mini pill

The mini pill is also known as the progesterone-only pill (POP). It differs from combined pills such as Mercilon as it only contains the progesterone 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 less side effects associated with it but it must be taken within either a 3 or 12 hour time period. For this reason, it has a realistic efficiency rate of 84% taking into account day to day factors. 

Alternatives to Mercilon

Gedarel and Munalea are two brands of the pill which contain the same hormonal components. Ovranette, Ovysmen and Tri-minulet are other types of the pill which are good for managing heavy and painful periods. The brands most likely to be prescribed by a GP 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.

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 progesterone only pill then you may need to wait until your period begins to switch contraceptive pill. Check with your doctor or pharmacist for instructions as it may vary depending on the type of pill you are on. 


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 everyday for three weeks before having a seven day break. This is when you have your period. If you skip the pill free week then you won't have a period until the following month. 

If I have vomited, will Mercilon still work?

Vomiting less than four hours after 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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