LivingHow do contraceptives work?

How do contraceptives work?


Contraception or birth control is a set of strategies to prevent pregnancy . There are different methods that try to achieve this, and they work in different ways. However, perhaps the most interesting thing about this broad topic is that there is no single method that works for everyone . Your choice of birth control should be based on several factors, such as your health, the frequency of your sexual activity, or your desire to have children in the future.

These help prevent fertilization of gametes (egg and sperm), which leads to pregnancy. This is also known as birth control. These medical tools and pills are called contraceptives. Broadly speaking, the main objective of a contraceptive is to prevent pregnancy. But some of them can also serve as protection against sexually transmitted infections/diseases ( STIs/STDs ).

The strategies

If a sperm penetrates an egg, pregnancy can occur , and birth control methods try to prevent this in a number of ways. Some try to prevent the egg from being released by the ovaries and, therefore, prevent it from being fertilized. Another method is not to prevent the release of the egg, but to prevent its formation in the first place. There is also the strategy of “barrier methods” , both male and female condoms, whose objective is to prevent the sperm from penetrating the body of the sexual partner. Although condoms are not the most effective methods, they are perhaps the most important, because in addition to preventing pregnancy they are also capable of preventing sexually transmitted diseases. This is something that other contraceptives do not achieve, so in all cases, a double barrier method tends to be recommended, that is, using a condom, at the same time as another of the methods that we will explain below.

Types of contraceptives

There are various kinds of tools , from the condoms we’ve mentioned, both male and female, to pills, cups, diaphragms, intrauterine devices (IUDs), progesterone-only pills, injections, contraceptive implants, contraceptive patches, and vaginal rings.

How do these contraceptives work?

There are about 4-5 broad categories of contraceptives. They include all the devices and contraceptives mentioned above.

The categories are: reversible contraception, hormonal methods, barrier methods, sterilization, and emergency contraception.

Reversible contraceptives:

Among long-acting reversible contraceptives we find intrauterine devices and implants are two types of long-acting reversible contraceptives.

Intrauterine devices (IUDs) are a small T-shaped device that is placed in the uterus to prevent pregnancy. The device is inserted by a medical professional and can stay in place for years and continue to function properly. A healthcare professional removes or replaces the device after the appropriate period has elapsed, or when the woman no longer needs or prefers another contraceptive method. There are two types of IUDs: the hormonal IUD and the copper IUD.

Implants are rods that can be inserted into the body. Each stick is the size of a matchstick, flexible, and made of plastic. The failure rate of this method is less than 1%. The doctor places the rod under the skin of the woman’s upper arm. The progestogen-releasing rod can be inserted for up to 5 years.

Hormonal methods:

Hormonal methods are short-acting forms of contraception. Hormonal contraceptives use hormones to prevent conception by regulating or stopping ovulation, and not all devices use the same hormones . The biological process by which the ovary releases an egg for fertilization is known as ovulation. Pills, injections, skin patches, transdermal gels, vaginal rings, intrauterine systems, and implanted rods are some of the ways that hormones can be delivered to the body. These treatments can inhibit ovulation , thicken cervical mucus, which helps restrict sperm access to the egg, or thin the lining of the uterus, depending on the hormones used. Hormonal contraceptives are prescribed and controlled by doctors.

We can find different types, such as injectable birth control, progestin pills or combined hormonal contraceptives.

Injectable birth control is a shot that is given once every three months. A progestin called Depo-Provera® (depot medroxyprogesterone acetate [AMPD or DMPA]) is injected into the arm or buttocks. This type of birth control, especially in adolescent girls, can cause a temporary reduction in bone density. However, after DMPA use is stopped, most of the bone loss reverses.

Progestin pills (PSPs) are a synthetic form of the hormone progesterone, which is produced naturally by the body. Progestins were designed to interact with progesterone receptors, in order to cause progesterone-like effects in the body.

Progestins were originally designed because natural progesterone is not well absorbed from pills and is metabolized too quickly in the body to have the desired effect. All forms of hormonal contraception have progestins, both progestin-only methods (such as the implant, hormonal IUDs, injection, or mini-pill) and combined hormonal contraceptive methods with an estrogen (such as the pill, patch, the vaginal ring and some injections).

The person takes one pill each day, preferably at the same time. These pills do not contain estrogen . These pills work by inhibiting ovulation and the elasticity of cervical mucus, making it difficult for sperm to reach the uterus or fallopian tubes. It is true that, by being able to alter the natural cyclical changes of the uterine lining, this treatment could cause unexpected or intermittent bleeding.

As for combined hormonal contraceptives , as the name itself indicates, it is a combination of estrogens and progresogens. It is worth mentioning that there are several types of estrogens, as well as progestogens, and the combinations of them are very varied. However, it is usually tried that the chosen combination has a low dose of Ethinyl Estradiol, an estrogen, since in low doses it is better tolerated.

There are 5 types of combined oral contraceptives:

  • Monophasic contraceptives: These have the same amount of estrogen and progestin in all active pills.
  • Biphasic contraceptives: The level of hormones in these pills changes once during each menstrual cycle.
  • Triphasic contraceptives: The dose of hormones changes every 7 days.
  • Quadriphasic contraceptives: The dose of hormones in these pills changes four times in each cycle.
  • Continuous or extended cycle contraceptives: These keep your hormone level up so you have few or no periods.

barrier methods

Barrier techniques, designed to prevent sperm from entering the uterus and are ” throwaway ” not implantable devices, may be a good alternative for couples who are unable or unwilling to use hormonal contraception. In all cases, however, condoms are recommended to avoid sexually transmitted diseases (STDs).

It is worth mentioning that condoms are not the only barrier methods available, and the failure rates of the different forms of barrier vary depending on the method in question.

Contraceptive sponges are soft, disposable, spermicide-filled foam sponges. Before intercourse, one is inserted into the vaginal canal. The sponge helps prevent sperm from entering the uterus, while the spermicide kills the sperm. After intercourse, the sponge should be left in place for at least 6 hours before being removed within 30 hours.

Spermicides , meanwhile, are chemicals that damage sperm. Spermicides can be used alone or with a cervical cap or diaphragm. A substance called nonoxynol-9 is the most common spermicidal agent (N-9). Foam, jelly, cream, suppository, and film are some of the strengths and forms available.

There are two other types of barrier methods that require a doctor’s visit and supervision , which are the diaphragm and the cervical cap. A diaphragm is a narrow, flexible cup made of latex or soft rubber that is inserted into the vagina to prevent sperm from entering the uterus. The diaphragm must be used with spermicidal cream before intercourse. They must remain in place for 6-8 hours and can be removed within 24 hours. The cervical cap is comparable to diaphragms, except that they are smaller and less flexible. The cervical cap is a tiny silicone cup that is placed in the vaginal canal before sexual activity to prevent sperm from entering the uterus. The cervical cap, like the diaphragm, must be used with spermicidal cream. The duration is the same as 6-8 hours and is removed after 48 hours.

As for condoms or “condoms” , there are both male and female condoms on the market. Male condoms are a thin sheath that surrounds the penis and collects sperm to keep it out of the woman’s body. Latex or polyurethane are the most commonly used materials in male condoms. As for female condoms, they are thin, flexible plastic bags. Before intercourse, a part of the condom is inserted into the woman’s vagina to prevent sperm from entering the uterus. The risk of STDs is also reduced with the use of the female condom.

emergency contraception

Emergency contraception is not a usual contraceptive strategy . If no other form of contraception has been used during intercourse or if the contraceptive technique has failed, for example if a condom has broken, emergency contraception can be used.

There are two commonly used emergency contraceptives: the emergency contraceptive pill and the copper IUD.

Emergency contraceptive pills , also known as the morning after pill, are hormonal pills that can be taken in one dose or in two doses 12 hours apart and are designed to be used during unprotected intercourse. The pills can postpone or prevent ovulation for at least 5 days if taken before ovulation, allowing sperm to remain inactive.

As for the copper IUD , it is a type of intrauterine device that can be inserted after unprotected intercourse. It is effective up to 5 days after the event.


Sterilization is a long-term contraceptive method that prohibits the woman from becoming pregnant or the man from releasing sperm. The sterilization operation, which usually involves surgery, must be performed by a health professional. Most of these operations are not reversible . In women, tubal ligation is used, in which the fallopian tubes can be tied (or closed) to prevent sperm and eggs from fertilizing. In men, the procedure used is vasectomy , which prevents the man’s sperm from reaching his penis, ensuring that his ejaculate never contains enough sperm to fertilize an egg.

What is the most effective method?

In order of effectiveness we have:

  1. Surgical sterilization
  2. Combined oral contraceptives
  3. IUD
  4. barrier methods
  5. Sponge
  6. Natural methods (based on monitoring the most fertile days within the menstrual cycle through knowing the cycle, measuring body temperature, etc.)
  7. Interrupted intercourse (“reverse”)

You may be surprised to learn that with some methods, 18-20 pregnancies per 100 women are recorded in 1 year , on average. Some of the methods that register these figures are “reverse gear” (22% ineffectiveness), spermicides (28%) and even male and female condoms (often because they are not placed correctly, are worn or are of poor quality ).

Some people calculate their most fertile days based on their menstrual cycle and refrain from intercourse during those days. This is not a reliable method, registering 24% of accidental pregnancies per year.

Among the methods that are really effective we find the irreversible ones (the surgical interventions mentioned) and, within the reversible ones, the implants (0.05%), hormonal IUD (0.2%), copper IUD (0.8%), injectables (6 %), pills, patches and rings (9%), or the diaphragm (12%).

Not everything is for everyone

Unfortunately, there are a number of contraindications specific to each method, the type of hormones used, whether the person in question is of one age or another, whether they are a smoker or not, etc. Regarding hormonal contraception, for example, blood pressure figures, body mass index, the presence of migraines (often these preparations can make migraines much worse), and other cardiovascular risk factors are taken into account, among others.

And these are just some of the factors to take into account, the matter becomes very complicated depending on your history of cancer, breastfeeding, lupus, diabetes, previous thrombosis, HIV, thyroid problems, etc. For this reason, the medical evaluation of the contraceptive methods that you could benefit from in your case is crucial.


Combined oral contraceptives (nd). MedlinePlus Medical Encyclopedia.

Contraception (2022). CDC: Centers for Disease Control and Prevention.

Ray, L. (2019). Introduction to progestins. Clue.

What are the different types of contraception? (2017). NIH: National Institutes of Health.


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