IUDs, uncovered: types, fit and side effects

The coil has a reputation that runs ahead of it, half whispered warnings, half glowing reviews. Let us sit down together and look at what an IUD actually is, what the fitting feels like, and which side effects are worth knowing, so the mystery turns into something you can hold in your hand.

⏱️ 7-minute read · Words by Chiara Ugozzoli · Updated June 2026

TLDR: “The coil” is really two devices. The copper coil (intrauterine device, or IUD) is hormone-free and works by releasing copper. The hormonal coil (intrauterine system, or IUS) releases a small amount of progestogen and tends to make periods lighter. Both are tiny T-shapes, both are over 99% effective, both last for years, and with both, your fertility returns the moment they come out. Side effects are most common in the first few months and usually settle. Here is the warm, honest picture.

So what exactly is a coil?

Let us clear up the biggest source of confusion first. When people say “the coil,” they could mean one of two devices, and they behave quite differently. The NHS describes the copper coil (the IUD) as a small plastic T-shape that a doctor or nurse places into your womb, working with zero hormones by releasing copper. It is over 99% effective, works as soon as it is fitted, and lasts for 5 or 10 years depending on the type. The NHS adds a detail many women find reassuring: a copper coil can even be used as emergency contraception, and it is safe to use while breastfeeding.

Its hormonal cousin, the IUS, is the same little T-shape but releases the hormone progestogen instead. The NHS hormonal coil page lists it as over 99% effective, lasting 3 to 8 years depending on the type, and you may recognise its brand names: Mirena, Levosert, Kyleena, Jaydess and Benilexa. It can usually be fitted soon after giving birth, and it is safe while breastfeeding too. Both coils are reassuringly reversible. With each one, the NHS confirms that fertility returns to its previous level straight away once the device is removed.

Picture this. A nurse holds up the device and it is barely the length of a matchstick, a soft little T about a quarter the size of your palm. Most women picture something far larger. That first glimpse, smaller and gentler than imagined, tends to take the edge off the whole idea.

Copper or hormonal: how do I tell them apart?

The cleanest way to choose between the two is to think about hormones and periods together, because that is where they truly differ. The copper coil is the hormone-free option, which appeals to anyone who would rather keep added hormones out of the picture. The trade-off lives in your cycle. The NHS notes that with a copper coil your periods may become heavier, longer or more painful, especially at first, though this often improves after a few months.

The hormonal coil tends to move periods the other way. The NHS says an IUS can make periods shorter or lighter, or stop them altogether, and it can even be an effective treatment for heavy periods. Some types are also used as part of hormone replacement therapy (HRT) during menopause, where the NHS says it has fewer side effects than other forms of progestogen. So the headline choice is refreshingly simple: prefer hormone-free and willing to accept possibly heavier periods, lean copper; want lighter periods and comfortable with a low dose of progestogen, lean hormonal. Many women find it helpful to think about what their periods are like right now, then picture which direction they would happily move. If heavy, painful periods already shape your month, the hormonal coil may feel like a double win, calming your cycle while it quietly handles contraception. If you simply want effective cover with your own natural rhythm intact, the copper coil keeps things hormone-free.

What does getting fitted actually feel like?

This is the part that fills the search bars at midnight, so let us be honest and kind about it. A trained doctor or nurse fits the coil during an appointment, and many women describe it as a few minutes of strong period-style cramping. The NHS lists period-like pain for a few days afterwards as a normal, expected experience for both the copper and hormonal coil.

A few small kindnesses help. Booking when you have a calm afternoon in place of a packed schedule means you can rest if you want to. Taking simple pain relief beforehand is something many women find useful, and you can ask your clinician what they recommend for you. Some women bring a friend, some plan a quiet evening with a hot water bottle and a favourite film. After fitting, some spotting and cramping for a few days is part of the settling-in. Your body is adjusting to a new resident, and it usually makes peace with it within weeks. Knowing how long protection takes to kick in helps too: the copper coil works straight away, while a hormonal coil may need a few days, so ask your clinician what applies to your timing.

Try this tonight: Write down two questions for your fitting appointment, for example “what pain relief can I take beforehand?” and “how soon will I be protected?” Pop them in your phone notes. Walking in with questions ready turns a nervous appointment into a conversation you are steering.

Which side effects are normal, and which mean call someone?

Most coil side effects are front-loaded into the first few months and then fade. For the copper coil, the NHS lists some bleeding between periods, periods that may become heavier or longer for a while, and a small chance of recurring thrush. For the hormonal coil, the NHS notes period-like pain and spotting after fitting, small harmless fluid-filled sacs (cysts) on the ovaries that usually clear on their own, and that same small chance of thrush. Many IUS users sail through it feeling free of side effects entirely. Some people mention headaches, acne, sore breasts or mood changes, and the NHS is candid that there is limited evidence on whether the IUS causes these.

One genuinely empowering habit is the thread check. Both devices have soft threads that sit high in the vagina, and learning to feel for them now and then is your simple at-home reassurance. The NHS guidance matters here: if you are unable to feel the threads, or they feel different, you might be less protected, so use another method and get checked. It is a quick, calming routine once it becomes familiar, a bit like checking a smoke alarm. Your partner should feel only the very tips of the threads at most, and the NHS says if they feel a problem, a quick clinic visit can sort it.

There are also rarer risks worth naming calmly. The NHS lists pelvic infection (usually within three weeks of fitting), the device moving or coming out (usually within the first few months), and in very uncommon cases damage to the womb. Seek urgent advice or call NHS 111 if you have lower-tummy pain that painkillers fail to ease, a high temperature, unusual or smelly discharge, very heavy bleeding, or you think you might be pregnant. These events are uncommon, and knowing the signposts means you can relax the rest of the time.

The gentle takeaway

The coil deserves a calmer reputation than it has. Two small devices, one copper and hormone-free, one hormonal and period-lightening, both quietly over 99% effective for years, both fully reversible the day they leave. The fitting is a brief, manageable moment, and the side effects mostly belong to the first few months. Take your questions, learn your thread check, and let your doctor, nurse or sexual health clinic help you choose the version that fits the life and the body you actually have.

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References

1. NHS. What is an IUD (intrauterine device) or copper coil? https://www.nhs.uk/contraception/methods-of-contraception/iud-coil/what-is-it/
2. NHS. Side effects of an IUD (intrauterine device) or copper coil. https://www.nhs.uk/contraception/methods-of-contraception/iud-coil/side-effects/
3. NHS. What is an IUS (intrauterine system) or hormonal coil? https://www.nhs.uk/contraception/methods-of-contraception/ius-hormonal-coil/what-is-it/
4. NHS. Side effects and risks of an IUS (intrauterine system) or hormonal coil. https://www.nhs.uk/contraception/methods-of-contraception/ius-hormonal-coil/side-effects-and-risks/

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PrettyWell is a women’s lifestyle and wellbeing magazine. This article shares general information and wellbeing perspectives to help you ask better questions and feel more in charge; for anything about your own health, please speak with a qualified healthcare professional.