Contraceptive Injections: How It Works, Side Effects & Benefits

What is a contraceptive injection?

Contraceptive injection is also known as Depo-Provera, which contains the hormone progestin to prevent pregnancy. 

How does a contraceptive injection work?

The contraceptive injection functions by preventing ovulation, a critical phase of the reproductive cycle during which an egg is released from the ovary. Additionally, it thickens the cervical mucus, creating a barrier that obstructs sperm from effectively reaching and fertilising the egg.

How effective is the contraceptive injection?

The contraceptive injection is 96% effective in preventing pregnancy, which means that about 4 unplanned pregnancies will occur out of every 100 women every year. 

Women at greatest risk of accidental pregnancy while taking contraceptive injection include younger women, particularly adolescents, which is related to not getting the injection on time or missing the injection. 

How long does contraceptive injection last?

This contraceptive injection is injected into your arm or buttock. It remains effective for approximately 12 weeks or 3 months, requiring a scheduled injection every three months to maintain its contraceptive efficacy.

How long does it take for a contraceptive injection to work?

The timing of your contraceptive injection determines how quickly it provides protection against pregnancy:

• During the first 5 days of menstruation: If you receive the injection within the first 5 days of your menstrual period, you'll be protected against pregnancy immediately, without needing additional contraception.

• At any other time: If you get the injection at any other point in your cycle, use an additional form of contraception, like condoms, for the first 7 days to ensure full protection.

Consult your gynaecologist for personalised advice and to ensure you’re using the injection effectively.

Where can I get contraceptive injections?

This contraceptive injection contains prescriptive medication which is only available in family planning clinics, women’s clinics, and some GP clinics.

How much is a contraceptive injection in Singapore?

In Singapore, the contraceptive injection typically costs between $150 to $200 for each 3-month dose. 

What are the pros and cons of using contraceptive injection?

Pros

• You do not have to remember to take it daily or during sex

• It provides long-term contraceptive protection as long as you get the shot on time (every 3 months)

• It does not interfere with sexual activity

• It is highly effective 

Cons

• It may cause irregular menses 

• Other side effects such as weight gain, acne, headache, hair loss, and excessive growth of facial and body hair

• It does not protect against sexually transmitted diseases (STDs)

• You need to stop taking contraceptive injections several months ahead of time if you plan for pregnancy

• You need to visit your healthcare provider regularly for contraceptive injections 

What are the side effects of the contraceptive injections?

The contraceptive injection, while effective for preventing pregnancy, can have side effects, which may vary among individuals. Common side effects include:

• Changes in menstrual patterns, such as irregular bleeding or spotting, heavier or lighter periods, or potentially no periods at all.

• Weight gain.

• Headaches.

• Mood swings or changes in emotional well-being.

• Decreased bone density with long-term use, which may increase the risk of osteoporosis if not managed.

• Soreness or bruising at the injection site.

• Potential delay in return to fertility after stopping the injections.

FAQ

When can I start using contraceptive injections after giving birth?

If you are not breastfeeding:

• You can receive the contraceptive injection immediately after giving birth.

If you are breastfeeding:

• The injection is usually given after 6 weeks to ensure it doesn’t affect milk production.

Timing for immediate protection:

• If you get the injection on or before day 21 after giving birth, you will be immediately protected against pregnancy.

• If you start the injection after day 21, you will need to use additional contraception, such as condoms, for the first 7 days to ensure full protection.

Your gynaecologist can offer personalised advice and support to help you choose the best time to start the contraceptive injection based on your individual situation.

When can I start using contraceptive injections after miscarriage or abortion?

You can start using contraceptive injections immediately after a miscarriage or abortion, and you will be protected against pregnancy right away.

If you have an injection more than 5 days after miscarriage or abortion, you will need additional contraception, such as condoms for the first 7 days after the injection.

Who is not suitable for contraceptive injection?

The contraceptive injection may not be suitable for everyone. Certain individuals should either avoid it or use it with caution under medical guidance. These include people who have:

• Unexplained vaginal bleeding 

• Liver disease 

• Breast cancer 

• Autoimmune diseases such as lupus 

• Circulatory problems such as heart attack or stroke 

Does contraceptive injection protect against STDs?

This contraceptive injection does not protect you against sexually transmitted diseases (STDs). To help protect yourself from STDs, use a male and/or female condom each time you and your partner have sex. 

Which is better: contraceptive injection or pill?

Choosing between the contraceptive injection and the pill depends on your lifestyle and preferences. Here’s a comparison to help you decide:

Contraceptive injection:

• Effectiveness: The injection provides slightly better pregnancy prevention, with about 6 in every 100 women becoming pregnant in the first year of use.

• Convenience: You receive the injection every three months, so you don't have to remember a daily pill.

Contraceptive pill:

• Effectiveness: The pill offers similar protection, with about 9 in every 100 women becoming pregnant in the first year of use.

• Routine: You need to take the pill daily, which requires consistency and can be challenging for some.

Both methods are effective, but the best choice depends on your personal needs and how well you can adhere to the routine. Discuss your options with your gynaecologist to determine which method suits you best.