Information about Medicines

An Update on Oral Contraceptives and Blood Clots

June 2000

Before prescribing a contraceptive, your doctor is required to discuss the options with you and to explain the risks and benefits. Your doctor will also need to check whether you have any risk factors that would prevent you from using an oral contraceptive (‘the Pill’) or increase your risk of having a blood clot or other side effect. All benefits and risks need to be considered when deciding which contraceptive is best for the individual woman.

This information is about blood clots that may, although very rarely, occur with some combined oral contraceptives.

What is a blood clot?

The blood clots associated with oral contraceptives occur in the veins of the legs and cause a blockage. They may cause death when pieces of the clot dislodge and travel to the lungs, but this happens rarely. (These blood clots are not those that may occur with your period.)

How often do blood clots occur with oral contraceptives?

Blood clots occur rarely with oral contraceptives, and deaths from blood clots are even more rare.

The risk of having a blood clot depends on a number of factors. It increases with age and is also affected by which pill is taken. For every 100,000 women taking the pill for a year, approximately 35 will develop a blood clot. One woman will die as a result of the blood clot. Compared to women not taking the pill, the odds of having a blood clot increase by 3-4 times for those on second generation pills and 6-8 times for those on third generation pills. Women using progestogen-only pills are thought to be at little or no increased risk of blood clots.

The following table lists the types of oral contraceptives available in New Zealand.

Type of oral contraceptive	Brands
Progestogen-only pill	Femulen, Microlut, Microval, Noriday
Combined oral contraceptives with low-dose oestrogen and progestogen or anti-androgen
Second generation Pills containing the progestogens levonorgestrel or norethisterone	Brevinor, Brevinor-1, Levlen, Loette, Microgynon 20ED/30/30ED, Monofeme, Nordette, Norimin, Synphasic, Trifeme, Triphasil, Triquilar
Other Pills containing the anti-androgen cyproterone	Diane-35
Third generation Pills containing the progestogens desogestrel or gestodene	Femodene, Marvelon, Melodene, Mercilon, Minulet
Combined oral contraceptives containing high-dose oestrogen and progestogen
Pills containing 50mcg oestrogen	Biphasil, Microgynon 50ED, Nordiol, Norinyl-1, Ovral

How often are blood clots fatal?

Of those who get a blood clot, about 3% will die. Given the wide use of oral contraceptives, two deaths a year from blood clots would be expected in New Zealand.

From 1990 -1999, 20 women using oral contraceptives died in New Zealand of a blood clot on the lungs. Of those who died, 15 were using third generation pills. The risk of death with second generation pills is lower but still present.

What increases the risk of blood clots?

Some of the risk factors for blood clots are a previous blood clot, a close family member who has had a blood clot, being overweight, cancer, recent surgery, being immobilised and bad varicose veins. Women who have had a previous blood clot should not take a contraceptive pill containing oestrogen. You should tell your doctor if any of these risk factors apply to you.

Your risk of having a blood clot can be increased temporarily, for example by a long flight, being immobilised by injury or illness, or by having surgery.

What are the symptoms and what should I do about them?

The symptoms of a blood clot in the leg are swelling, tenderness and pain, but a blood clot may occur without symptoms. Breathlessness and sharp chest pain can occur with a blood clot on the lungs. These symptoms can also occur for other reasons.

If you are taking an oral contraceptive pill and you develop any of these symptoms you should see a doctor immediately. You should be particularly alert to these symptoms if you have a risk factor for blood clots.

Your doctor may refer you to hospital for tests and treatment with blood-thinning medication. Treatment may last for several months and some women may have ongoing problems such as pain or swelling.

Who should I discuss this information with?

You should discuss your risk of blood clots with your doctor. There are a number of different types of contraceptives available, including non-hormonal barrier methods e.g. condoms. You should discuss with your doctor which type is likely to suit you best. You have a right to expect your doctor to explain this information in a way that you can understand.

Remember that blood clots are rare events in healthy women taking the contraceptive pill. Serious consequences are even more unlikely to occur. Your risk will be reduced even further if you see a doctor immediately if you get any symptom of a possible blood clot.