How does it take for the birth control shot to become effective?

Answer 1

That first answer is pretty nice & lengthy! :-p The info is all correct though.

PERSONALLY, I am on Depo Provera. When I got my first shot, I was informed that Depo-Provera can require up to fourteen days to take effect. This means pregnancy can occur within fourteen days of the first Depo injection.

I'll add a Wikipedia entry for you if you'd like more info!

Answer 2

Sexual Health: Your Guide to Birth Control: Depo-Provera
Birth control is a way for men and women to prevent pregnancy. There are many different methods of birth control; some types also protect against sexually transmitted diseases. Depo-Provera does not protect against sexually transmitted diseases.

Depo-Provera is a birth control method for women. It is made up of a hormone similar to progesterone and is given as a shot by a doctor into the woman's arm or buttocks. Each shot provides protection against pregnancy for up to 14 weeks, but the shot must be received once every 12 weeks to remain fully protected.

How Soon Does It Work?
Protection begins immediately after the first shot if given within the first five days of your menstrual period.

How Effective Is Depo-Provera?
Depo-Provera is 99% effective in preventing pregnancy. However, it does not prevent spreading of STDs. To help protect yourself from STDs, use a latex male condom each time you and your partner have sex.

Can Any Woman Use Depo-Provera?
Most women can use Depo-Provera. However, it is not recommended for women who have:

Unexplained vaginal bleeding
Liver disease
Breast cancer
Blood clots
Are There Side Effects Associated With Depo-Provera?
Depo-Provera can cause a number of side effects, including:

Irregular menstrual periods, or no periods at all
Headaches
Nervousness
Depression
Dizziness
Acne
Changes in appetite
Weight gain
Excessive growth of facial and body hair
Hair loss
Loss of bone mineral density
Most of the side effects are not common. Change in the menstrual cycle is the most common side effect. You may experience irregular bleeding or spotting. After a year of use, about 50% of women will stop getting their periods. Their periods usually return when they discontinue the shots.

Prolonged use of Depo-Provera may result in loss of significant bone mineral density, increasing the risk of osteoporosis. This risk is more likely for those who have been taking it for longer than 2 years, particularly when other risk factors for osteoporosis exist, such as family history and chronic alcohol and/or tobacco use. Although there are no studies to benefit its use, it is advised that all women on Depo-Provera get adequate calcium and Vitamin D (through diet and/or supplements) to help prevent osteoporosis.

Can I Become Pregnant After I Stop Using Depo-Provera?
With Depo-Provera, you could become pregnant as soon as 3 to 4 months after your last shot. However, it may take some women up to a year or two to conceive after they stop using this type of birth control. This time frame seems unrelated to how long you have been using Depo-Provera for contraception.

What Are the Advantages of Using Depo-Provera?
There are several advantages to using Depo-Provera:

You don't have to remember to take it every day or use it before sex.
It provides long-term protection as long as you get the shot every three months.
It doesn't interfere with sexual activity.
It's over 99% effective.
It's less expensive than the Pill.
What Are the Disadvantages of Using Depo-Provera?
Disadvantages to using Depo-Provera include:

It can cause unwanted side effects.
It does not provide protection against sexually transmitted diseases.
It can cause irregular menstrual periods.
You need to stop taking Depo-Provera several months ahead of time if you plan to become pregnant.
Regular doctor visits can be inconvenient.
Talk to your doctor to determine if Depo-Provera is right for you.

Reviewed by the doctors at The Cleveland Clinic Department of Obstetrics and Gynecology.

Answer 3

At least 2 weeks. I would use condoms for a few weeks to be sure.