Mercilon is a hormonal birth control pill belonging to the category of combined oral contraceptives with its two active ingredients, ethinylestradiol and desogestrel which are synthetic bioequivalents of naturally occurring sex hormones oestrogen and progesterone respectively. Developed and marketed by Merck Sharp and Dohme pharmaceutical company in the UK, Mercilon contains the same active ingredients as Marvelon, but in a somewhat lower dose which makes this contraceptive tablet suitable for women who are somewhat more susceptible to side effects of the medicine. Just like its higher dose equivalent, Mercilon is taken continuously for 21 days, followed by a one week break before the cycle begins again.

What’s on this page?

How reliable is Mercilon?

Despite its somewhat lower dose as compared to other combined contraceptive pills on the UK market, Mercilon is just as effective, providing 99% protection against pregnancy. And as a combination contraceptive pill, it is somewhat more reliable that progesterone-only alternatives. However, in order to ensure maximum protection against unwanted pregnancy when using Mercilon, you should use the pills properly, in line with the instructions provided by your prescriber. This means that you should never miss a pill and that you should carefully follow the pattern of 21 day taking the pills followed by 7-day long break before the new cycle begins. It is also important to be aware of other medications and remedies which can compromise the protection offered by Mercilon. These include:

  • Epilepsy treatments
  • HIV or AIDS medications
  • High blood pressure drugs
  • St John’s wort
  • Ciclosporin
  • Lamotrigine

Additional information about how to ensure maximum protection with Mercilon can be found in the official patient information leaflet that is issued within every pack of the medicine.

How does Mercilon prevent pregnancy?

Hormonal birth control pills all rely on synthetic, man-made versions of naturally-occurring sex hormones, progesterone and oestrogen. The active ingredients of Mercilon, ethinylestradiol and desogestrel, will effectively mimic the natural hormones and via that mechanism of action, they will interfere with the natural processes related to menstrual cycle, but also to various preparations for pregnancy that female body goes through during every cycle, regardless of whether conception will actually take place. However, the aforementioned sex hormones play different roles in the female body and as such, the compounds mimicking them will act to decrease the chances of unwanted pregnancy in different ways.

Why does Mercilon contain desogestrel?

Naturally occurring progesterone is absolutely crucial in timing and triggering ovulation, the process during which an egg cell is released by the ovaries to the fallopian tubes where it can get fertilised by sperm. If the conception takes place, the fertilised egg cell will travel to the womb and implant into the uterine wall where it will continue to develop. With this in mind, it comes as no surprise that synthetic progesterone acts by tricking the body into wrongly detecting that the ovulation had already taken place, thus preventing the ovaries from releasing egg cells.

Why does Mercilon contain ethinylestradiol?

On the other hand, synthetic oestrogen will provide additional protection in case the primary one, stemming from synthetic progesterone. It will contribute to the thickening of the cervical fluids and changes in the conditions alongside the uterine wall. These processes will help prevent unwanted pregnancy in different way – the change in consistency of cervical fluids will make it harder for the sperm to reach the egg cell and the changes in the uterus will make it less likely for the fertilised egg cell to implant.

Can I buy Mercilon online in the UK?

Just like other birth control pills, Mercilon is a prescription-only medication and as such, it can be obtained only with a valid prescription issued by a certified medical professional. However, today this is not an obstacle to buying the treatment online. In the UK, there are numerous online pharmacies that will allow you to do exactly that – order your treatment from the comfort of your home, after consulting with a doctor through specialised apps or functions of the online clinic’s website.

In most cases, you will be asked to fill in a detailed and customised medical questionnaire that the doctor will use in order to assess you suitability for using Mercilon. Once the doctor gets a detailed insight into your medical profile and history, he will be able to make an informed decision. Once you get the green light, the prescription will be issued and used to have the contraceptive pills delivered from the partner pharmacy to the address you provided in a discreet, plain packaging. If Mercilon still appear to be too intrusive for you, some lower-concentration alternative such as Microgynon might be prescribed.

How to take Mercilon?

In order to ensure maximum protection when using Mercilon, you should always precisely adhere to the instructions provided by your prescriber and to the guidelines outlined in the official patient information leaflet that you can find within your pack of Mercilon.

Below, we will present you a short and illustrative overview of some of the most general things you must keep in mind when taking this contraceptive pill. Please note that as such the text below cannot be used as a substitute for the official information, nor the doctor’s instructions. Instead, it is here simply to help you get a better understanding of what taking Mercilon might look like.

  • One pack contains three strips, thus covering three monthly cycles
  • Full monthly cycle lasts 28 days
  • For the first 21 days, you will be taking one Mercilon tablet each day at the same time
  • After taking the 21st tablet you will have depleted the full strip
  • Proceed by taking seven days off (without taking any pills)
  • After the 28th day, commence a new treatment which will look exactly the same
  • Take the tablets whole with water, never chew or break them
  • Use the arrows and labels on the strip to keep track of your treatment and ensure you are on course
  • Those taking Mercilon for the first time should consult the patient information leaflet on how and when to commence treatment
  • If you miss a dose, consult the leaflet about how to proceed

What are Mercilon side effects?

Common (1 in 100 women) Rare (1 in 1000 women)
·       Migraines

·       Headaches

·       Weight fluctuations

·       Breast tenderness

·       Rash

·       Upset stomach

·       General malaise

·       Depression

·       Libido changes

·       Heart problems

·       Circulation problems

·       Fluid retention

·       Irregular vaginal secretions

·       High blood pressure

·       Gallstones

·       Chorea

·       Worsening of systemic lupus

·       Pancreatitis

·       Crohn’s disease

·       Ulcerative colitis

·       Worsening of otosclerosis

·       Blood sugar issues

·       Porphyria exacerbation




Please note that this is not a full list of all documented side effects. We would implore you to consult the official patient information leaflet for a more comprehensive overview.