Why choose a 20mcg combined contraceptive pill instead of 30mcg pill?

The development of low dose pills

When the combined pill was first developed in the 1950s, it contained a comparatively high dose of oestrogen, 150 micrograms of mestranol. However as clinical experience with the pill accumulated, it was realised that the same contraceptive effect could be obtained using far lower doses of hormones.

Over the past 60 years, in order to improve the safety of the pill, and to reduce the side effects, the types of hormone in the pill have been altered, and the dose of hormones lowered dramatically. There are now a wide variety of different pill brands with differing doses and differing hormone combinations.

Most combined contraceptive pills today contain 30 or 35 micrograms of the oestrogen ethinylestradiol which is twice as potent as mestranol, so approximately equivalent to 60 or 70 micrograms of mestranol, that is less than half the original oestrogen dose used for contraception.

Some combined pills contain even lower doses of ethinylestradiol, 20mcg, and these are often called low dose pills.

What do we know about 20mcg pills?

• 20mcg combined pills contain 30% less oestrogen than most other combined pills. However these are still a recommended and reliable form of contraception.

  There is no evidence that 20mcg pills are less effective, although pill failures have been seen to be increasing generally, in more recent clinical trials. This is thought to be due to modern trials using normal pill taking populations rather than the stricter regimes of early trials. 20mcg pills do give safe reliable contraception, but for some women, the added safety of a standard 30mcg pill, may be preferable. Long-Acting Reversible Contraception (LARC) such as implants, injections and coils (IUD and IUS) are the most reliable modern contraceptives and the overall hormone doses used are even lower again.

• All the low dose combined pills are third generation pills. More information about the difference between second and third generation pills.

• The low dose 20mcg combined pills are supplied in 21-day blister packs, and the standard regime is to take one pill daily for 21 days and then take a 7-day break, during which time there is usually a period-type bleed.

• When taking a low dose 20mcg combined pill, it is also possible to use a modern, off label, tailored regime. The blister packs can be tricycled or you can use a flexible extended regime in the same way as for any combined contraceptive pill. However, there is possibly a greater chance of irregular bleeding or spotting if using one of these extended regimes with a low dose pill.

• Logically it would seem that the thrombosis (blood clot) risk should be less with a 20mcg pill than with a 30mcg pill, but this has been difficult to prove in clinical studies. However these pills have been shown to cause fewer damaging changes to the blood clotting system itself.

• Lowering the oestrogen dose is not suitable for everyone, and may result in side effects such as bleeding. Oestrogen can be beneficial. It tends to improve acne, and also helps stabilise bleeding patterns.

• A 20mcg pill may be helpful for example if a standard (30mcg or 35mcg) pill causes nausea or vomiting. These are usually an oestrogenic side effect.

• Bleeding patterns are slightly less favourable with 20mcg pills (study), and more favourable on 30mcg pills (study).

• 20mcg pills may only be prescribed subject to the same medical recommendations as 30mcg pills. Even though they contain a lower dose of oestrogen, they are still generally regarded as having the same risks and benefits as other pills.

• Fit, healthy, non-smoking, women can use any combined pill until they are 50. It may be an option to reduce to a 20mcg pill in older women, whose natural fertility is declining with age, and for whom a lower dose of oestrogen may reduce cardiovascular/stroke risk. Any change in contraceptive pills should be discussed with your usual GP or sexual health advisor.

Where can I get a 20mcg pill?

All combined contraceptive pills are prescription only medicine (POM).

• Make an appointment with your GP/practice nurse.
• Visit NHS - Find a Sexual Health Clinic – type in your postcode to find the nearest specialist clinic to you.
• Dr Fox are only able to prescribe combined contraceptive pills you are already taking, so if you want to swap to a new combined pill brand, you must see your doctor/nurse or visit a clinic.

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