What you should know about the birth control shot before trying it
- You only have to take the birth control shot four times a year, making it a more convenient alternative to the pill for people who are comfortable with injections.
- The birth control shot is an injection of progestin, which can come with side effects including spotting, headaches, bloating, and minor weight gain.
- Certain people should not use the birth control shot like people with breast cancer, liver disease, and fragile bones.
- This article was medically reviewed by Jamie Lipeles, DO, founder of Marina OB/GYN in Marina Del Rey, California and Olivia P. Myrick, MD, who is a clinical assistant professor with the Department of Obstetrics and Gynecology at NYU Langone.
For those who struggle to remember taking their birth control pill on time, the birth control shot may sound like a desirable alternative. With the shot, you only have to think about birth control four times a year. As long as you're comfortable with injections, it may be a contraceptive to consider.
The shot is effective for 14 weeks
The birth control shot, Depo-Provera, is an injection of progestin, one of the hormones found in birth control pills. It was approved by the US Food and Drug Administration in 1992 and remains the only approved birth control shot in the US today.
According to the US Department of Health and Human Services, the shot prevents pregnancy "by keeping the ovaries from releasing eggs. It also causes cervical mucus to thicken and the lining of the uterus to thin. This keeps sperm from reaching and fertilizing an egg."
The shot is given every 12-14 weeks, or four times a year. As long as you get the shot on time, it's 99% effective at preventing pregnancy, says Kari Braaten, MD, the medical director of the Fish Center for Women's Health at Brigham and Women's Hospital. The 1% chance of pregnancy is attributed to human error — for example, not getting the shot on time. By comparison, the pill is only 91-93% effective.
The shot releases progestin into your bloodstream, and, like the pill, it works by suppressing your natural ovulation. But unlike the pill, the shot is a single dose once every three months, rather than a daily dose.
"Because it's one dose, it can only last so long," says Braaten, adding that at approximately 14 weeks, hormone levels become low enough that some women can have their natural ovarian function return to normal, and with that comes ovulation and fertility.
"So we know, based on the studies that have been done, that no women are at risk of pregnancy in the 12- to 14-week window," says Braaten.
Health care providers will often give the first shot within seven days of starting your period to ensure you're not pregnant when injected. For those who don't get the initial injection during their period, they should use a backup method of birth control in the following seven to 10 days.
Generally, you have to visit a doctor's office to get the shot. However, there is a subcutaneous, or under-the-skin, injection you can give yourself called Depo-Subq Provera 104. However, due to low demand, it is less readily available than Depo-Provera and not covered by many insurance carriers.
Common side effects include spotting and weight gain
Common side effects of the birth control shot include:
- Headaches
- Bloating
- Irregular menstrual bleeding
- Weakness and fatigue
- Weight gain
Many women also don't get their period while taking the shots. And, after one year, about 50% of women have no bleeding, Braaten explains. But, that's perfectly normal and safe.
"The reason why people don't get a period is because the lining of the uterus that normally has to shed does not build up when you have that hormonal influence from the shot," Braaten says. "You don't bleed because there's just nothing to come out."
Weight gain on Depo-Provera
The average weight gain amongst those who experience this side effect is approximately five pounds, according to the American College of Obstetricians and Gynecologists. Yet, Braaten says there's a lot of variability. "Some women gain a lot more weight, and some women do not gain any weight."
In fact, the birth control shot is the only contraceptive method proven to make women gain weight. While doctors are still unsure what causes the large variation in weight gain while using the shot, they do know it's probably a result of underlying genetic variations.
Who should not get the birth control shot
If you'd like to get pregnant within the next year, this birth control method may not be for you. Experts say it could take 10 months or more to get pregnant after stopping the shots.
Braaten says the earliest return to ovulation is about 16 weeks, "but for many women the effect of the birth control lasts for much longer, and normal ovarian function doesn't return for quite a bit longer."
The birth control shot should also be avoided if you have certain medical conditions including:
Breast cancer
Many forms of hormonal birth control, including the shot, are not recommended for women with breast cancer, as breast cancers can be hormonally responsive. This means the cancer cells grow in response to estrogen or progesterone. Speak with your doctor if you have breast cancer to determine which method of birth control is best for you.
Liver disease
People with liver disease should also avoid the shot. "Hormones are processed or metabolized in the liver, so people with severe liver disease are not allowed to have any hormones," Braaten says.
History of heart attack or stroke
Women with a history of heart attack or stroke are not advised to use Depo-Provera, according to Mayo Clinic. In general progesterone-only contraceptives are not associated with blood clots, stroke, or heart disease. But because the injection is a slightly higher dose it's best to err on the side of caution, says Braaten.
Fragile bones
A downside of the shot is that the injection suppresses your natural estrogen levels. Women with underlying bone loss rely on estrogen to bolster their bone density. Therefore, Braaten says those who are at risk for bone loss should not use Depo-Provera.
Hypothalamic amenorrhea
People who have the condition hypothalamic amenorrhea, or don't regularly get a period because of low-body fat percentage, also shouldn't get the shot. Braaten says that's because they don't produce enough estrogen on their own so they should opt for an estrogen-containing contraceptive.
Depo-Provera, bone loss, and osteoporosis
Depo-Provera has a warning on its packaging saying that the product might increase the risk of osteoporosis and shouldn't be used for more than two years.
This warning was added after multiple studies showed a strong correlation between the shot and loss of bone density. Researchers said the reason was likely because the active ingredient in the shot, called medroxyprogesterone, can decrease the calcium stored in bones.
However, in 2005 the World Health Organization brought together experts to review the effects of hormone contraception on bone health. They concluded there should be no restriction on the use or duration of the birth control shot in women ages 18-45.
"They also concluded that among females younger than 18 years and women older than 45 years, the advantages of using DMPA [depot medroxyprogesterone acetate] generally outweigh the theoretic safety concerns regarding fracture risk," the American College of Obstetricians and Gynecologists states.
Additional research has shown that the shot is safe to use for longer periods of time and that bone density returns as soon as the Depo-Provera is discontinued. In fact, a 2007 review published in Contraception found bone density returned to normal as early as 24 weeks after stopping use and persisted.
Ultimately, Braaten says the shot is safe to use for more than two years. "There are a lot of women who fear this warning about bone loss and are told that they can't be on it for more than two years," Braaten says. "One of the important messages is there is not — for healthy women — a time limitation on how long you can stay on it if it is the best method for you."
Benefits of the birth control shot
While you do have to remember your quarterly shot, the injection is less time consuming than daily birth control pills.
Some women favor the birth control shot because it doesn't interrupt sex — meaning, no more worrying about condoms or diaphragms. They also may experience fewer cramps and lighter periods, or possibly none at all.
"It can provide very good bleeding control for people who have problems with heavy periods," Braaten says.
Furthermore, the shot only contains progesterone, while other contraceptive methods like the pill usually contain additional hormones, like estrogen. So this progesterone-only option is ideal for women with medical conditions that can't use combined contraception that contains estrogen, like the ring or patch, says Braaten.
With any birth control, there are risks and benefits. So talk to your doctor about the best method for you.