How Long After Getting The Depo Shot Is It Effective (And Why)?

Exact Answer: Immediately

The Depo shot is the common term of reference used to connote the Depo-Provera injection that is used as a form of birth control in women. This injection is given on a regular schedule to women in order to substitute the use of other contraceptive measures.

The main ingredient in the injection is depot medroxyprogesterone acetate. The concoction is made with a certain type of progesterone that acts as an effective contraceptive measure by preventing conception for 14 weeks. The Depo shot is administered in the arm or buttocks of the patient. However, the shot is only effective against pregnancy, and not against STDs.

How Long After Getting The Depo Shot Is It Effective

How Long After Getting The Depo Shot Is It Effective?

The Depo shot is known for its efficient efficacy. The concoction of the shot starts working immediately in women who take it within the first 5 days of their periods. Thus, if the Depo-Provera shot is administered to a patient within the initial week of her new cycle, it will become effective immediately.

However, this is not the case if the individual in question delays her shot. If a woman takes the Depo shot after the first 5 days of her period, she will have to wait for a week for the shot to become effective. This implies that the woman in question may become pregnant within this window of time if she engages in sexual intercourse.

Therefore, it is always advisable that when women opt for the shot after the initial 5-day window of their periods, they must use some other form of contraception to avoid pregnancy during the first week after the shot has been administered.

Once active, the shot remains effective for 13 to 14 weeks. After the lapse of this period, the individual must go back for the shot. However, if she misses this window and goes back after 15 weeks or more, a pregnancy test may be necessary to confirm that she has not conceived in the interim window.

Although this timeline is more or less fixed, it is always better to consult your primary healthcare provider or gynecologist before opting for the shot. You may have certain medical considerations to be evaluated before you can start taking the Depo shots.

In summary:

Depo Shot TimeBeginning of Efficacy
Within the 5th Day of the CycleImmediately
Any Other Time During the Cycle7 to 10 days later

Why Is The Depo Shot Effective So Soon After Getting It?

The Depo-Provera shot is designed to help stop pregnancy by targeting the ovulation of the woman in question. Ovulation is that stage in the menstrual cycle when an egg is released from the ovaries to be fertilized into an embryo.

The Depo shot works by affecting the process of ovulation in the patient. If no ovulation takes place, then there can be no fertilization. It also thickens the cervical mucus of the woman. This prevents the sperm from successfully reaching the egg and thereby negates the possibility of fertilization.  

When the shot is taken within the initial days of the cycle, it is well in time to stop the release of an egg since ovulation happens around the 10th to 14th day of a cycle. This implies that a woman who has taken the shot within this time frame is ensured protection.

However, if the shot is taken during other stages of the cycle, it may not be able to block ovulation effectively. This is because the egg may have already been released from the ovary. Thus, it can only thicken the cervical mucus at this stage and this requires at least a week.

This shot is a highly effective method of pregnancy prevention. Only less than 1% of women who used the Depo shot have conceived while on the drug. However, doctors do not recommend that patients remain on it for more than 2 years especially if they can use other methods of contraception. Moreover, it is not a protector against STIs, which also acts as a deterrent for most.


As an injectable form of birth control, Depo-Provera is used by many women across the world. The popularity of this method of contraception is due to the convenience attached to it. It can guarantee long-lasting effectiveness with just a single shot that needs to be taken 3 months apart.

It is known that a Depo shot will become effective immediately in the patient if it is taken within the first 5 days of her period. Otherwise, it can take a week for the shot to become effective. However, after the first seven days, it becomes effective and remains so for the next 13 weeks.


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