How hormonal contraceptives like the pill work

The hormones in contraceptives don’t only prevent ovulation. Some also prevent fertilized eggs from implanting into the womb. Others cause the mucus in the cervix (the opening of the womb) to become thick and sticky, making it harder for the sperm to move and reach the egg cell.

Hormonal contraceptives are only reliable if they are used properly. If, for instance, a woman forgets to take her pill one day, her ovaries may release an egg (ovulation) and she could become pregnant.

The effectiveness of hormonal contraceptives may be reduced by medication such as antibiotics, blood-pressure-lowering or cholesterol-lowering drugs, antifungal drugs or herbal products like St. John’s wort. Also, if women who take the pill vomit or have diarrhea, the pill may no longer provide enough protection. So they have to use another form of contraception too – for instance, a condom.

What are the advantages and disadvantages of hormonal contraceptives?

The biggest advantage of hormonal contraceptives is their reliability: Studies have shown that only about 1 out of 1,000 women get pregnant per cycle if they take the pill or use a contraceptive skin patch or vaginal ring properly.

Hormonal contraceptives can also relieve period pain, and often lead to lighter periods. If a teenage girl or woman has acne, the hormones may improve her skin too.

The potential disadvantages include side effects such as headaches, nausea, sore breasts and vaginal yeast infections (thrush). The hormones can also cause spotting between periods or lead to mood swings, and may reduce women’s sexual desire.

And there is a small risk of blood clots forming (thrombosis). This risk is higher in women over the age of 40, as well as in women who smoke, are very overweight, or have a higher risk of vascular disease in their family.

Third- and fourth-generation birth control pills (such as those containing desogestrel, dienogest, gestodene and drospirenone) appear to increase the risk of thrombosis more than older first- and second-generation pills do (such as those containing levonorgestrel or norgestimate). It is estimated that thrombosis occurs within one year in

• about 9 to 12 out of 10,000 women who regularly take a birth control pill containing desogestrel, gestodene or drospirenone.
• about 5 to 7 out of 10,000 women who regularly take a birth control pill containing levonorgestrel or norgestimate.

For comparison, thrombosis occurs in about 2 out of 10,000 women who aren’t on the pill.

Although claims to the contrary are often made, there is no scientific proof that hormonal contraception makes women gain weight.

The birth control pill

Most birth control pills contain a combination of the hormones estrogen and progestin, which is why they are also called “combined pills” or “combination pills.” Different pills have different doses of hormones in them and are taken in different ways. But all birth control pills are taken on 21 or 22 days per cycle.

There are one-phase, two-phase and three-phase pills – sometimes also referred to as monophasic, biphasic and triphasic pills. With one-phase pills, each pill in the packet contains the same amount of hormones in the same proportions. With two-phase pills and three-phase pills, the pills in the packet have different doses and proportions of hormones in them, depending on the phase of the cycle. They have to be taken in the correct order to work properly. In most cases, if a woman forgets to take one pill, she has to take it within the next 12 hours. Otherwise continuing to take the pill will not reliably prevent pregnancy for the rest of her cycle.

After taking them for 21 or 22 days, there is a 6- or 7-day break during which the monthly period occurs. Pregnancy will still be prevented during this break. Some birth control pills have 28 pills per packet and are taken every day, to make it easier for women to take them properly. The last six or seven pills in the packet don’t have any hormones or drugs in them, though.

There is also a less commonly used kind of pill called the “mini pill.” The mini pill only has progestin in it, in low doses, so it can also be used by women who don’t tolerate the combined pill well. But more discipline is needed to take it properly: The mini pill has to be taken at the same time every day. If women don’t take a pill at that time, they have to take it within three hours. Because it is taken continuously, without breaks, many women stop getting their periods after a while.

The contraceptive skin patch

The contraceptive skin patch is about 5 cm by 5 cm in size, and very thin. It can be placed on the woman’s behind, belly, the outside of her upper arm or anywhere on her upper body – with the exception of her breasts. It’s important to make sure that it sticks to the skin properly and doesn’t rub against clothing too much. Activities like having a shower, a bath or swimming usually don’t make it come off. In the first three weeks of the cycle, the patch is replaced once a week. No patch is used in the fourth week. The woman then gets her period. A new patch is stuck onto the skin seven days after removing the old patch. If it is stuck on 24 hours too late, it is no longer a reliable form of contraception.

Just like most birth control pills, the patch contains a combination of the hormones estrogen and progestin. Whereas the hormones in the pill enter the bloodstream through the digestive system, the hormones in the skin patch are absorbed by the skin and enter the bloodstream in that way. More estrogen enters the body through the patch, so the patch can have more side effects than the pill and the vaginal ring. Research has shown that women who use the skin patch are more likely to stop using it because of side effects than those who are on the pill.

The vaginal ring

The vaginal ring is about 5 cm in diameter and is made of a soft, flexible synthetic material. Like the combined pill and skin patch, it also contains a combination of estrogen and progestin. These hormones are absorbed into the bloodstream through the wall of the vagina. The ring is inserted deep into the vagina and is taken out again after exactly three weeks, using a finger. The woman then has a period during the “ring-free” days that follow, and a new ring is inserted after exactly seven days. If the ring is inserted properly, the woman can’t feel it.

In order to reliably prevent pregnancy, the ring must be inserted and removed at the same time on the same weekday. For example, if a woman first inserts the ring at 10 p.m. on a Wednesday, she should remove it again at 10 p.m. on the Wednesday three weeks later, and insert a new ring at 10 p.m. on the Wednesday after that. But it’s also okay to do so up to three hours before or after that time.

Research has found that, compared to the pill, the vaginal ring generally has fewer side effects such as nausea, irritability and depression. But ring users had more vaginal infections (vaginitis) than women who took the pill.

Hormone-releasing contraceptive coils

Hormone-releasing coils are made up of a T-shaped plastic device and a string that is used to pull them out. They contain and continuously release the hormone levonorgestrel, which is absorbed by the lining of the womb. Levonorgestrel stops the lining of the womb from building up, which means that any fertilized eggs aren’t able to become embedded in the lining of the womb. It also makes the mucus in the cervix (opening of the womb) thicker and stickier, preventing sperm from getting into the womb. Hormone-releasing coils are inserted by a doctor or nurse. An ultrasound scan is then done to make sure that the coil is in the right position.

Because of the continuous absorption of hormones, most women’s periods become lighter, and many women stop getting their periods altogether after a few months. The coil starts working as soon as it is in place. It prevents pregnancy for three to five years, depending on the exact type of coil used.

Sometimes the coil moves out of place, so regular check-ups are recommended. Side effects such as spotting, headaches and nervousness are fairly common in the first few weeks after inserting the coil. Rare side effects include pelvic infections or injury to the wall of the womb.

The hormone-releasing coil usually isn’t recommended in women who haven’t had children because it’s harder to put the coil into their womb. It is also thought that the risk of infection is lower after giving birth.

Other hormonal contraceptives

Other, less common, hormonal contraceptives include the three-month injection and the hormonal birth control implant. The injection has to be given every three months. Although it is a very reliable form of contraception, it is often not well tolerated because of the high dose of hormones used. Hormonal birth control implants look like small rods and are implanted under the skin every three years. This is done by a doctor. These two forms of contraception are usually only recommended for women who can’t tolerate other hormonal contraceptives or can't use them regularly.

Weighing the pros and cons

All forms of hormonal contraception are similarly effective at preventing pregnancy. A woman’s choice of contraception may depend on how well she tolerates the different kinds, and how she feels about the potential side effects. Another factor is what the contraceptive method involves: Does she mind swallowing a pill every day? Would wearing a patch on her body for several weeks bother her? Can she feel the vaginal ring inside her during sex? Women have to find out for themselves what is most important to them and which method they tolerate the best.

As well as hormonal contraceptives, there are also non-hormonal contraceptives. You can get more information about the different kinds of contraceptives from your doctor or women’s health center.

Sources

• Beckermann MJ, Perl FM (Ed). Frauen-Heilkunde und Geburtshilfe. Basel: Schwabe; 2004.
• Bundesinstitut für Arzneimittel und Medizinprodukte (BfArM). Rote-Hand-Brief zu kombinierten hormonalen Kontrazeptiva, einschließlich Informationsmaterialien: Risiko von venösen Thromboembolien. February 03, 2014.
• Bundeszentrale für gesundheitliche Aufklärung (BzgA). Familienplanung.de: Verhütungsmethoden. 2017.
• Bundeszentrale für gesundheitliche Aufklärung (BzgA). Sichergehn. Für sie und ihn. Cologne, 2016.
• European Medicines Agency (EMA). Ethinylestradiol + drospirenone-containing oral contraceptives (YASMIN, YASMINELLE and other products) – Risk of venous thromboembolism. May 26, 2011.
• Lopez LM, Grimes DA, Gallo MF, Stockton LL, Schulz KF. Skin patch and vaginal ring versus combined oral contraceptives for contraception. Cochrane Database Syst Rev 2013; (4): CD003552. [PMC free article: PMC7154336] [PubMed: 23633314]

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