Reviewed by a GPhC-registered Pharmacist at Newdays Pharmacy
Quick Answer: The contraceptive injection (Depo-Provera or Sayana Press) delivers a progestogen hormone that prevents pregnancy for twelve to thirteen weeks. It is over 99 percent effective, contains no oestrogen, and is suitable for women who cannot or prefer not to use oestrogen-containing contraception. The most important consideration is that fertility may take twelve to eighteen months to return after stopping. It is not ideal for women who may wish to conceive within the next year or two.
What Is the Contraceptive Injection?
The contraceptive injection contains medroxyprogesterone acetate, a synthetic progestogen hormone. There are two formulations available in the UK:
- Depo-Provera (150 mg): Administered as an intramuscular injection (into the muscle, usually the buttock) by a healthcare professional
- Sayana Press (104 mg): Administered as a subcutaneous injection (under the skin of the lower abdomen or thigh), which can be self-administered at home after training
Both formulations are given every twelve to thirteen weeks (approximately every three months). The slightly lower dose in Sayana Press is formulated for subcutaneous delivery and is bioequivalent to the intramuscular dose.
How Does the Contraceptive Injection Work?
The contraceptive injection works primarily by preventing ovulation. The continuous release of medroxyprogesterone acetate suppresses the hormone signals that would normally trigger egg release. It also thickens cervical mucus, making it difficult for sperm to reach the egg, and thins the lining of the uterus.
How Effective Is the Contraceptive Injection?
The contraceptive injection is over 99 percent effective at preventing pregnancy with perfect use. In typical use, it is one of the most reliable forms of contraception available, as there is no daily or weekly action required by the user. Provided the injection is given on time (within the correct window), it is highly reliable.
What Are the Advantages of the Contraceptive Injection?
- Does not contain oestrogen: Suitable for women who cannot take oestrogen
- Long-acting: A single injection lasts twelve to thirteen weeks
- No daily action required: Nothing to remember daily or weekly
- Privacy: No pills, patches, or devices to store
- May reduce period-related symptoms: Many women experience lighter periods or no periods at all after starting the injection
- Suitable during breastfeeding: Safe to use from birth
What Are the Disadvantages of the Contraceptive Injection?
Delayed Return of Fertility
This is the most significant drawback of the contraceptive injection. After stopping, it can take twelve to eighteen months for fertility to return fully. Some women wait up to two years before their periods and fertility return to normal. This is because medroxyprogesterone acetate is stored in fatty tissue and released slowly over time after the last injection. If you are planning to conceive in the near future, the injection is generally not recommended.
Irregular Bleeding
Irregular, unpredictable bleeding is very common in the first six to twelve months of using the injection. Many women then experience very light periods or no periods at all (amenorrhoea), which many find acceptable or desirable. However, some women find persistent irregular bleeding difficult to manage.
Bone Mineral Density
Prolonged use of the contraceptive injection is associated with a temporary reduction in bone mineral density. This is usually reversible after stopping, but the FSRH advises that the benefits and risks of continuing the injection for more than two years should be reviewed, particularly in young women (under 18) whose bones are still developing and in women over 40 approaching the menopause.
Not Immediately Reversible
Unlike most other contraceptive methods, the effect of the injection cannot be quickly reversed. If side effects occur, they may persist for the duration of that injection dose.
Who Is the Contraceptive Injection Suitable For?
- Women who want long-term contraception without daily effort
- Women who cannot take oestrogen-containing contraception
- Women who are breastfeeding
- Women who have difficulty remembering to take a daily pill
- Women who want lighter or no periods
Who Should Consider an Alternative?
- Women who may wish to conceive within the next one to two years
- Women with a history of depression (some evidence suggests the injection may worsen mood in some individuals)
- Women with osteoporosis or significant risk factors for bone loss
Getting the Contraceptive Injection at Newdays Pharmacy
The contraceptive injection can be administered at Newdays Pharmacy by our trained GPhC-registered pharmacists at our branches in Eton (Windsor), Twyford, Reading (Coley Park), and Lane End, subject to a clinical consultation. Sayana Press self-injection can also be supplied and trained for home use.
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Clinical Disclaimer: This article is intended for general information only and does not constitute medical advice. Always consult a qualified healthcare professional before starting any treatment or medication. Information is accurate as of the date of publication and reviewed by a GPhC-registered pharmacist. Newdays Pharmacy is registered with the General Pharmaceutical Council (GPhC).
Frequently Asked Questions
Depo-Provera should ideally be given every twelve weeks. It can be given up to fourteen weeks from the previous injection without additional precautions in most cases. If more than fourteen weeks have passed, you may need to use additional contraception for seven days and consider emergency contraception if relevant. Speak to your pharmacist or clinician promptly if you think you may have had an injection late.
Periods often become irregular or stop altogether with the injection, but this is not guaranteed. Approximately 50 percent of women have no periods after one year of use, rising to approximately 70 percent after two years. Some women continue to have irregular bleeding throughout.