Combined contraceptive pills are the most reliable form of contraception, being effective in as much as 99% of cases when used properly, in line with the doctor’s instructions and the official guidelines. This type of oral contraceptive contains synthetic versions of naturally-occurring sex hormones progesterone and oestrogen. The manmade pharmaceutical compounds used in this type of birth control medication are highly adept at mimicking the activity of their naturally-synthesised counterparts. As such, they can easily take their function and “trick” the body in various ways in order to achieve the desired results.

What’s on this page?

How reliable are combined contraceptive pills?

For as long as you use them properly, combined birth control medications will be 99% efficient, with practically no risk of unwanted pregnancy. However, it is important to note that there are certain medications and other substances that have been known to impair the functionality of these contraceptives.

So, in order to ensure optimal levels of protection, be sure to avoid the following:

  • Epilepsy medications
  • Bosentan
  • Antibiotics
  • HIV medications
  • Aprepitant
  • Fosaprepitant
  • Modafinil
  • Barbiturates
  • St John’s wort
  • Metoclopramide
  • Medical charcoal
  • Colesevalem
  • Ciclosporin
  • Slegiline
  • Tizanidine

Of course, in some situation it won’t be possible to avoid some of these medications. In that case, you will have to use additional barrier contraceptives for as long as the protection provided by your oral contraceptive is impaired. The exact duration of the impairment will depend on the exact type and brand of birth control pill you will be taking.

How do combined contraceptive pills work?

In order to prevent unwanted pregnancy, combined birth control pills will mimic the activity of naturally-occurring sex hormones, thus interfering with the processes in the female body that make pregnancy possible. The first and probably most important precondition for conception is ovulation, a process marked by the release of the egg cell from the ovary and its subsequent movement to the fallopian tube where it can get fertilised in case of an unprotected intercourse.

This process is timed and triggered activity of progesterone or more precisely, the levels of progesterone detected by the body, so it comes as no surprise that combined oral contraceptives rely on synthetic progesterone in order to trick the body into “believing” that ovulation already took place, so the egg cell will not get released. This is possible because the body will be unable to differentiate between naturally-synthesised progesterone and the presence of man-made analogues which are the active ingredients of all contraceptive pills, both combined and single-agent ones.

At the same time, oestrogen whose analogues are present in combined oral contraceptives plays an important role in enabling the egg to implant in the uterine wall. So, this active ingredient of combined contraceptive pills, synthetic oestrogen, will change the environment alongside the uterine wall, making it much more difficult for the egg to actually implant. At the same time, these synthetic hormones will increase the thickness of cervical fluids, making it harder for sperm to reach the egg cell even if it gets released.

In total, all of these mechanisms of action act in tandem to make conception 99% less likely to occur. However, in practice, synthetic progesterone alone will be effective enough to prevent ovulation at the first place, thus making secondary lines of defence provided by synthetic oestrogen de facto unnecessary.

What combined contraceptive pills can I buy in the UK?

You can learn more about different combined contraceptive pills available on the UK market here:

What are the side effects of combined oral contraceptives?

Prescription medications are regulated in the UK with a good reason. Just like most of them, oral contraceptives come with risk of certain side effects and it is highly advisable to get familiar with them prior to commencing treatment so that you will be able to act accordingly. By doing so, you will make sure that you will be able to differentiate between those side effects which will require you to halt treatment and seek immediate medical advice and those which are uncomfortable, but not really dangerous (as such, they will not necessarily require cessation of the treatment. The former include:

  • Swelling or tenderness in the abdomen
  • Coughing up blood
  • Sharp and severe pain in the chest
  • Sudden shortness of breath or painful breathing
  • Inflammation of the veins in the legs
  • Migraines (without prior history)
  • Dizziness
  • Sight or speech problems

Other possible side effects which are not considered to be particularly dangerous include:

  • Upset stomach
  • General malaise
  • Changes of appetite
  • High blood pressure
  • Weight fluctuations
  • Depression
  • Breast pain or tenderness
  • Changes of libido
  • Irregular vaginal bleeding

Please note that the exact side effects will depend on the specific contraceptive you will be using.