Article produced in association with Spital Clinic

Both the copper coil and the Mirena are more than 99 per cent effective as contraceptives — but they work in completely different ways, have opposite effects on periods, and suit very different people.

With the FSRH’s May 2024 licence extension for the Mirena now in effect, this guide covers the five key differences using up-to-date UK evidence, not the older guidance that many sources still repeat.

How Each Device Works

The FSRH March 2023 guideline set out the terminology now used across UK clinical practice: the copper intrauterine device (Cu-IUD) and the levonorgestrel intrauterine system (LNG-IUD).

The copper coil works by releasing copper ions that are toxic to sperm, preventing fertilisation. It contains no hormones at all, making it a strong option for women who cannot or do not want hormonal contraception.

The Mirena — the most widely prescribed 52mg LNG-IUD in the UK — thickens cervical mucus to block sperm, thins the uterine lining, and may suppress ovulation, though most users continue to ovulate normally.

According to Hull University Teaching Hospitals NHS Trust, the hormone levels it produces are lower than those from the combined contraceptive pill — relevant for women advised to avoid higher-dose hormonal methods.

The hormone-free nature of the Cu-IUD is its defining advantage for some; the localised hormonal action of the LNG-IUD is its defining advantage for others.

According to NHS guidance on the copper coil, neither device interacts with medicines or herbal remedies, and both can be fitted in women who have never been pregnant.

The way each device works also determines what it does to periods — often the deciding factor.

Effectiveness and Duration

The NHS confirms both devices prevent pregnancy in more than 99 per cent of users. When it comes to contraceptive effectiveness, there is no meaningful difference between them.

Where they differ significantly is duration. The copper coil lasts up to 10 years, and one fitted in a woman aged 40 or over can remain in place until menopause under FSRH March 2023 guidance.

For the Mirena, the picture changed in May 2024: the FSRH CEU statement on extended LNG-IUD use confirmed that all 52mg LNG-IUDs — including the Mirena, Levosert, and Benilexa — are now licensed for eight years of contraceptive use, up from five under previous guidance.

When the Mirena is used as part of HRT, it protects the uterine lining for up to five years before requiring replacement. Smaller-dose devices such as Kyleena (20mcg) are licensed for five years, and Jaydess for three.

Both are long-acting reversible contraceptives — fertility returns immediately after removal, with no delay or washout period. Both are available without a GP referral through the coil insertion and removal service at Spital Clinic.

What Each Device Does to Periods

The most important practical difference is what each device does to periods — and they go in opposite directions.

The copper coil typically makes periods heavier, longer, and more painful; the NHS notes this may ease after a few months, but heavier bleeding is one of the most common reasons for early removal.

Both devices can cause irregular spotting in the first three to six months after fitting.

The Mirena does the opposite.

According to Hull University Teaching Hospitals NHS Trust, it reduces monthly blood loss by 86 per cent at three months and by 97 per cent at twelve months.

Nine in ten women who use it for heavy periods see a significant reduction; around 20 per cent have no bleeding at all; and 80 per cent report meaningful pain relief.

NHS information on the hormonal coil confirms that periods often become lighter, shorter, and less painful — with many users finding they stop entirely after the initial settling-in period.

For women whose choice of contraception is being shaped by troublesome periods, those statistics make the direction of the decision clear.

For women with already disrupted cycles, it is worth booking a private specialist assessment before deciding — for this group, the choice of coil is as much a treatment decision as a contraceptive one.

Unlike the copper coil, the Mirena is licensed as a first-line treatment for menorrhagia — heavy or prolonged bleeding defined as losing more than 80ml per cycle or periods lasting longer than seven days.

In around half of cases, heavy periods have no identifiable structural cause, making the Mirena’s targeted local action particularly useful: it reduces bleeding at the endometrial level without surgery, general anaesthesia, or high-dose systemic hormones, and offers a non-surgical alternative to procedures such as endometrial ablation.

Side Effects, Risks, and Who Cannot Use Each Device

Both devices carry the same procedural risks. Pelvic infection affects around 1 in 100 women in the first three weeks; expulsion happens in roughly 1 in 20; and uterine perforation occurs in approximately 2 in 1,000 fittings — slightly higher in women breastfeeding within six months of delivery. Ectopic pregnancy, though rare, is a risk if either device fails.

The side-effect profiles diverge beyond those shared risks.

The copper coil carries no hormonal side effects — heavier periods are its main downside. The

Mirena may cause acne, headaches, mood changes, breast tenderness, and ovarian cysts; most resolve without treatment, but they are worth considering for anyone sensitive to progestogen.

The Mirena is also unaffected by vomiting, diarrhoea, or most drug interactions.

Each device has its own contraindications. Neither should be fitted in the presence of an active sexually transmitted infection or unexplained uterine bleeding.

The Mirena is not suitable for women with a history of breast cancer, certain liver conditions, serious cardiovascular disease, or certain uterine abnormalities.

The copper coil, meanwhile, can be used as emergency contraception if fitted within five days of unprotected sex — the only intrauterine option for post-coital protection.

The Fitting Procedure and What to Expect

The fitting procedure is the same for both devices: a 10 to 15 minute clinical appointment, ideally towards the end of a period, though it can happen at any point in the cycle.

The full appointment takes around 30 minutes. Local anaesthetic gel or spray is used to manage discomfort, and the NHS advises taking ibuprofen or paracetamol about an hour beforehand.

No surgery or general anaesthetic is needed. Some cramping and light spotting in the days after fitting is normal and usually settles within a week. Neither device requires you to have had children previously.

Fertility returns immediately after removal of either device — there is no waiting period before trying to conceive.

For most women, the choice between the copper coil and the Mirena comes down to one question: are hormones acceptable or not?

The copper coil suits women who want hormone-free contraception, those who cannot use progestogen, and those who need emergency post-coital protection.

The Mirena suits women who want lighter or absent periods, those managing menorrhagia, and those using it as the progestogen component of HRT.

Both offer equivalent contraceptive effectiveness and full reversibility.

The FSRH’s May 2024 extension of the Mirena’s licence to eight years makes it a stronger long-term option than many comparisons suggest — worth knowing if the information you have found is based on older guidance.

This article is produced for informational purposes only and does not constitute medical advice, diagnosis or treatment. Clinical guidance referenced reflects published NHS and FSRH standards as at March 2025. Individual circumstances vary; readers are advised to consult a qualified healthcare professional before acting on any information in this article.

This piece was produced in association with Spital Clinic, which provided background clinical information for editorial purposes. Hyperlinks to external sources are included for reference only and do not represent an endorsement of any product, service or organisation.