How do contraceptive injections work?
The injection releases progestogen into your bloodstream, which:
- Stops ovulation (so no egg is released for sperm to fertilise)
- Thickens cervical mucus, making it harder for sperm to reach an egg
- Thins the lining of the womb, making it less likely for a fertilised egg to implant
What are contraceptive injections used for?
They are mainly used to prevent pregnancy, but they can also help:
- Reduce heavy or painful periods
- Offer a discreet contraceptive method (nothing to remember daily)
- Provide an alternative for those who can’t use oestrogen-based contraception
Who can have contraceptive injections?
Most women and people with a uterus can have contraceptive injections, including those who can’t take the combined pill. It’s often recommended for those who want a long-lasting option without daily reminders.
Who might not be able to have contraceptive injections?
This method might not be suitable if you:
- Are pregnant or think you might be
- Have unexplained vaginal bleeding
- Have a history of breast cancer
- Have severe osteoporosis (as the injection can reduce bone density over time)
Can I use contraceptive injections if I’m pregnant or breastfeeding?
You shouldn’t have the injection if you’re already pregnant. If you’ve recently had a baby, it’s safe to use while breastfeeding, but it’s always best to check with a doctor or nurse first.
What if I miss my next injection?
If your next injection is late, you may not be fully protected against pregnancy. You might need to use extra contraception (like condoms) or take a pregnancy test before having your next dose. Speak to a healthcare provider for advice.
How effective are contraceptive injections?
They’re more than 99% effective when used correctly, meaning fewer than 1 in 100 people using it will get pregnant each year. Each injection lasts between 8 and 13 weeks, depending on the type.
Can you overdose on contraceptive injections?
Overdosing isn’t an issue as the injections are given at controlled doses by a healthcare professional. If you’re worried about side effects, speak to your doctor or nurse.
How often do I need the injection?
The usual schedule depends on the type of injection you have:
- Depo-Provera – every 12 weeks
- Sayana Press – every 12–14 weeks (can be self-administered at home)
- Noristerat – every 8 weeks (less common in the UK)
Are there any side effects?
Some people don’t notice any side effects, but possible ones include:
- Changes in periods (irregular, lighter, or stopping altogether)
- Weight gain
- Headaches
- Mood changes
- Reduced bone density (if used for a long time)
Side effects usually improve over time. If they don’t, speak to a healthcare provider about alternative contraception options.
How is the injection given?
A healthcare professional usually gives the injection into your upper arm or buttock. If you use Sayana Press, you may be shown how to give it yourself in the thigh or stomach.
When should I get my first injection?
Your first injection is usually given within the first five days of your period. This means you’ll be protected straight away. If you get it at another time, you may need to use additional contraception (like condoms) for seven days.
What are the brand names for contraceptive injections?
You may know the injection by these names:
- Depo-Provera
- Sayana Press (self-administered option)
- Noristerat (less commonly used in the UK)
Final thoughts
Contraceptive injections are a convenient and effective birth control option if you want long-lasting protection without daily reminders. They can affect your periods, so it’s worth considering whether that works for you. If you’re unsure, speak to a doctor or nurse to see if it’s the right choice for your lifestyle.
