What Is an IUD and How Does It Work?

Complete Healthcare Team

An IUD is one of the most effective forms of birth control available, right alongside sterilization, and yet a lot of people aren’t quite sure how the little T-shaped device actually prevents pregnancy. The short version: there are two very different kinds that work in two different ways, and the right one for you depends less on effectiveness (they’re all excellent) and more on what you want your periods and hormones to do.

If you’re weighing whether an IUD fits your life, understanding how each type works is the place to start. The family planning team at Complete Healthcare helps patients think through this decision regularly, and this guide covers what an IUD is, the types available, how effective they are, and the side effects worth knowing about.

What an IUD Actually Is

An IUD, short for intrauterine device, is a small, flexible, T-shaped device that a provider places inside the uterus to prevent pregnancy. It’s a form of long-acting reversible contraception (LARC), which means it works for years at a time but can be removed whenever you choose, with fertility typically returning quickly afterward.

There are two main categories: hormonal IUDs and the copper IUD. Both are placed the same way and both are highly effective, but what happens once they’re in place is quite different.

The Two Types of IUDs

Hormonal IUDs

Hormonal IUDs release a small amount of a progestin hormone called levonorgestrel directly into the uterus. In the United States, the FDA-approved hormonal IUD brands are Mirena, Liletta, Kyleena, and Skyla. They differ mainly in hormone dose and how long they last:

• Mirena: highest hormone dose, approved for up to 8 years
• Liletta: same 52 mg dose as Mirena, one of the longer-lasting options
• Kyleena: lower hormone dose, up to 5 years
• Skyla: lowest dose and smallest device, up to 3 years

The Kyleena IUD is a popular middle option for people who want a lower hormone dose than Mirena but longer protection than Skyla. It’s smaller than Mirena, which some people prefer, and lasts five years.

The Copper IUD

The copper IUD, sold under the brand name Paragard, contains no hormones at all. Instead, a thin copper wire wrapped around the device does the work. It’s approved for up to 10 years, making it the longest-lasting option, and it’s a good fit for people who want to avoid added hormones by preference or for a medical reason.

How Each Type Prevents Pregnancy

This is the heart of the question, and the two types genuinely work differently.

Hormonal IUDs prevent pregnancy mainly by thickening the mucus on your cervix, which blocks sperm from reaching an egg. The progestin also thins the uterine lining, and in some people it partially suppresses ovulation, though many people with a hormonal IUD do still ovulate. Because the hormone acts mostly right where it’s placed, the amount circulating through the rest of your body is lower than with birth control pills.

The copper IUD works without any hormones. Copper creates an environment in the uterus that’s toxic to sperm, impairing their ability to move and reach an egg. It also triggers a mild local inflammatory response that further prevents fertilization. Your natural cycle and ovulation continue as usual.

One useful thing to know: the copper IUD is also the most effective form of emergency contraception available when placed within five days of unprotected sex, and you can keep it afterward as ongoing birth control.

How Effective Is an IUD?

Both types are more than 99 percent effective at preventing pregnancy, which puts them among the most reliable methods there is. In practical terms, the CDC reports that fewer than 1 in 100 IUD users become pregnant in the first year of typical use. Hormonal and copper IUDs are both in this top tier.

Part of what makes them so effective is that, unlike the pill, patch, or ring, they don’t depend on you remembering anything. Once an IUD is in place, there’s nothing to take daily or refill, which removes the human-error factor that lowers the real-world effectiveness of many other methods.

Can you get pregnant with an IUD? It’s rare, but not impossible. No method except abstinence is 100 percent effective. If pregnancy does occur with an IUD in place, there’s a higher chance it could be ectopic (implanting outside the uterus), which is a medical situation that needs prompt attention. IUDs also don’t protect against sexually transmitted infections, so pairing one with condoms is worth considering if STI protection is a concern.

Side Effects Worth Knowing About

Being honest about tradeoffs matters here, because the side effects differ by type.

Hormonal IUD side effects often include changes to your periods. Many people find their periods get much lighter over time, and some stop having them altogether, which a lot of people consider a benefit, especially if heavy or painful periods are an issue. In the first few months, irregular spotting is common as your body adjusts. Some people report headaches, breast tenderness, mood changes, or acne related to the progestin.

Copper IUD side effects run in the other direction. Because it doesn’t change your hormones, your periods continue, and they can become heavier, longer, or crampier, particularly in the first several months. For some people this eases with time, and for others it’s the reason they choose a different method.

Does an IUD Cause Weight Gain?

This is one of the most common concerns, so it’s worth addressing directly. The evidence does not show a clear link between IUDs and meaningful weight gain. Copper IUDs, which contain no hormones, are not associated with weight gain at all. For hormonal IUDs, manufacturer data suggests only a small percentage of users report weight gain, and studies have not found it to be significantly different from what happens without an IUD. When weight changes do happen, they’re often related to other life factors rather than the device itself. In our practice, we talk this through honestly, because deciding based on a myth isn’t in anyone’s interest.

Common Questions About IUDs

Which IUD is best for heavy periods?

A higher-dose hormonal IUD like Mirena or Liletta is often chosen for this reason, because thinning the uterine lining tends to reduce menstrual bleeding significantly over time. The copper IUD is generally not the choice here, since it can make periods heavier. That said, “best” depends on your full health picture, so it’s a conversation worth having with a provider.

Will a hormonal IUD stop my periods completely?

It might, and for many people it does, particularly with the higher-dose options after the first year. Others keep having light periods. There’s no way to predict exactly how your body will respond, and keep in mind that even if your period stops, you may still ovulate, so a hormonal IUD isn’t a guaranteed fix for hormone-related symptoms like PMS.

How much does an IUD cost?

Under most insurance plans, IUDs are covered at little or no cost, but coverage varies by plan and by which device you choose. Our staff can help verify your specific benefits before your appointment so there are no surprises, and there are options worth exploring if you’re uninsured.

Which IUD Might Fit You

A quick orientation to help you see yourself:

• Want lighter periods or relief from heavy bleeding? A hormonal IUD, often a higher-dose one, tends to be the fit.
• Prefer to avoid added hormones? The copper IUD is the hormone-free option.
• Want the longest-lasting protection? The copper IUD lasts up to 10 years.
• Want hormonal benefits at a lower dose? Kyleena or Skyla offer lower progestin doses.

Talking Through Your Options

Choosing an IUD is a personal decision, and the best way to sort through it is a conversation with a provider who can factor in your health history and what you want from your birth control. Complete Healthcare offers family planning care with same-day appointments available across our 11 locations in Central Ohio, including Columbus, Pickerington, Newark, Lancaster, Marion, Marysville, and Delaware. Call us at 614-882-4343 or schedule online to talk it through.