Some birth control methods, such as condoms, diaphragms, and other barrier options, work right away. Birth control that makes chemical or physical changes to the body often takes longer, however.

A person should ask their doctor if they need to abstain from intercourse, and how likely a pregnancy is, both before and after a birth control method reaches its full effectiveness.

How long it takes a birth control method to begin working, depends on how it prevents pregnancy. Condoms, for example, provide birth control by preventing semen from entering the vagina. These and other barrier methods work immediately.

Fast facts on how long birth control takes to work:

  • The time it takes to work depends on the type, when it is used, and personal factors.
  • Methods that work by preventing ovulation can take several days to become effective.
  • No birth control method works 100 percent of the time for everyone.
  • Each method can also cause side effects that vary with overall health and individual lifestyle.

There are at least two ways to measure the effectiveness of birth control.

Correct or perfect use tells how effective a method is when it is used exactly, as recommended, every time. Typical use is a measure of how effective birth control is with the normal level of error most users experience.

The effectiveness of various methods, as well as how long they take to work, is as follows:

Oral contraceptives

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Oral contraceptives may be 99 percent effective when taken daily.

When they are used correctly, for example, taken daily, without missing a dose, oral contraceptives are 99 percent effective.

At typical usage rates, including being taken incorrectly at times, these drugs are 91 percent effective.

The progestin-only pill contains a hormone called progestin. This hormone thickens cervical mucus, making it more difficult for sperm to travel to an egg. It can also prevent ovulation.

If the first pill is taken within the first 5 days of the start of a woman's menstrual cycle, in other words, the first day of her period, it works immediately.

Women who have a cycle shorter than 23 days, however, will need to wait 2 full days. When taking the first dose later than 5 days after the first day of the cycle, these pills take 2 days to be effective.

Combination pills contain two hormones that prevent ovulation. The first pill is taken on the Sunday following a woman's period. These pills take 7 days to become fully effective.

Intrauterine device

An intrauterine device (IUD) is a small device inserted into the uterus. With typical usage, these devices are more than 99 percent effective.

The copper IUD causes inflammation in the uterus that kills sperm. It begins working immediately after a doctor inserts it, and can remain effective for up to 12 years. Hormonal IUDs such as Liletta, Mirena, and Skyla prevent ovulation with the hormone progestin.

If inserted within 7 days of the start of a woman's period, these devices are effective immediately. When they are inserted at any other time, they take 7 days to begin working.

Implants

Birth control implants are tiny rods that a doctor inserts under a woman's skin. They release progestin and prevent ovulation. At typical usage rates, these devices are more than 99 percent effective.

When inserted during the first 5 days of a woman's cycle, the implant works immediately. Otherwise, it takes 7 days to reach full effectiveness.

Patches

The birth control patch gives the body a dose of estrogen and progestin. Together, these hormones prevent the body from ovulating. A woman must apply a new patch each week, except during the week she gets her period.

The success rate is 91 percent in most women, but in those who weigh more than 198 pounds, failure may be more common.

When the first patch is applied within 5 days of the start of a woman's period, it works immediately. Otherwise, it takes 7 days to become effective.

Barrier methods

Barrier methods are methods that stop sperm from coming into contact with an egg, so preventing fertilization.

The male and female condoms and the diaphragm each create a physical barrier. With typical use, diaphragms are 88 percent effective. Female condoms are 79 percent effective, and male condoms are 82 percent effective.

Spermicides create a barrier by killing sperm. They are 72 percent effective with typical use.

Barrier methods begin working immediately.

Vaginal ring

The vaginal ring is a ring inserted into the vagina that releases estrogen and progestin. Like other hormonal methods, it prevents ovulation. A woman wears it for the first 3 weeks of her cycle and then takes it out to have her period.

With typical usage, the failure rate is 9 percent. If inserted on the first day of a woman's cycle, it works immediately. Otherwise, it takes 7 days to work.

Birth control injections

Birth control injections require an injection of the hormone progestin every 3 months. With typical usage, the success rate is 94 percent. The injection prevents ovulation. When the injection is given within 5 days of the start of a woman's period, it works immediately. Otherwise, it takes 7 days.

Vasectomy

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The effectiveness of a vasectomy will be nearly 100 percent, once a doctor has confirmed that the man is sterile after the procedure.

A vasectomy prevents sperm from getting into a man's semen. He can still ejaculate, but the ejaculate will not cause his partner to become pregnant. Initially, a man's fertility declines slowly and steadily following a vasectomy. For most men, there are no sperm in the semen by the 12-week mark.

One study, however, found that 17 percent of men still have sperm at 24 weeks following surgery. So, it is vital to continue testing semen with a doctor until it can be confirmed that sperm are no longer present.

The success rate of vasectomy is nearly 100 percent, as long as a man uses a backup method until a doctor confirms that he is sterile.

Female sterilization

Two methods can permanently sterilize a woman. Both are nearly 100 percent effective.

With transcervical sterilization, a doctor inserts a tube into each fallopian tube. This irritates the tubes, causing scar tissue that blocks the tubes and prevents an egg from being able to move down the tube. Transcervical sterilization takes about 3 months to work.

A tubal ligation is sterilization that also blocks the fallopian tubes but by surgically closing them. It is effective immediately.

Hormonal birth control might not be right for smokers and those with a history of blood clots, while sterilization should be reserved only for people who are certain they do not want any more children.

It is advisable to talk to a doctor about various options and to ask whether lifestyle or other factors will influence the effectiveness of the method a person chooses.