The combined oral contraceptive (COC) pill contains two hormones, oestrogen and progestogen. It may be taken by women to prevent pregnancy. Sometimes, the COC pill may also be taken for:

• painful or heavy periods,

• premenstrual syndrome, or

• endometriosis.

The main types of COC pill are described below.

Standard strength oestrogen: 21 day

As the name suggests, standard strength oestrogen pills contain a standard strength of oestrogen (30-35 micrograms) together with a progestogen. Each pack contains 21 pills. A pill is taken every day for three weeks, then there is a pill-free break for seven days, then a new pack of pills is started.

One brand of the COC pill (Norinyl-1) contains an oestrogen called mestranol. It is a slightly higher strength than the others but has the same effect as a standard strength COC pill.

If the pills are all the same colour, they contain the same amount of oestrogen and progestogen throughout the cycle. They're sometimes called monophasic pills.

If the pills are different colours, they contain different amounts of oestrogen and progestogen depending on the stage of the cycle. They're sometimes called biphasic or triphasic pills.

Standard strength oestrogen: 28 day or every day (ED)

Standard strength oestrogen pills contain a standard strength of oestrogen (30-35 micrograms) together with a progestogen. Each pack contains 28 pills: 21 active pills and seven inactive or 'dummy' pills. A pill is taken every day for 28 days, and then a new pack of pills is started. There is no pill-free break.

If the active pills (first 21 pills) are all the same colour, they contain the same amount of oestrogen and progestogen throughout the cycle. They're sometimes called monophasic pills.

If the active pills (first 21 pills) are different colours, they contain different amounts of oestrogen and progestogen depending on the stage of the cycle. They're sometimes called biphasic or triphasic pills.

The inactive pills (last seven pills) are white and lare arger than the active pills.

Low strength oestrogen: 21 day

Low strength oestrogen pills contain a low strength of oestrogen (20 micrograms) plus a progestogen.

Each pack contains 21 pills. A pill is taken every day for three weeks, then there is a pill-free break for seven days, then a new pack of pills is started.

The low strength oestrogen COC pill may be considered if you're at risk of developing blood clots, but are otherwise suitable for a COC pill. (See the 'special considerations' section.)

Dianette

Dianette (also called co-cyprindiol) is a special type of pill that's used when women want a treatment for acne or unwanted hair growth, and also want contraception. For routine contraception, the COC pills described above are preferred.