Does the copper coil cause weight gain?

What the research says

The copper coil is hormone-free. It contains no oestrogen, no progestogen, and no other systemic medication. It works by releasing copper ions into the womb, which create an environment that is hostile to sperm. Because it does not interact with your hormonal system, there is no biological mechanism by which the copper coil would directly cause weight gain.

Clinical studies back this up. A 2014 Cochrane review looking at hormonal and non-hormonal contraceptives found no significant weight change attributable to the copper IUD. Controlled trials comparing copper IUD users with non-users have consistently found no meaningful difference in weight over time.

This is one area where the copper coil has a genuine advantage over hormonal methods. The Mirena, the implant, and the injection have all been associated with modest weight changes in some women, likely mediated through progestogenic effects on appetite, fluid retention, or fat distribution. The copper coil does not carry this risk.

So why do some women gain weight after getting a copper coil?

Because weight gain happens for lots of reasons, and the timing is often coincidental.

Women tend to have a copper coil fitted at particular life stages: after having a baby, when coming off the pill, in their late twenties and thirties when metabolic rate naturally begins to slow. All of these are periods when weight change is common regardless of contraceptive method.

Coming off the combined pill is a particularly common confounder. The combined pill suppresses androgens and can reduce appetite and fluid retention in some women. When you stop it and switch to a hormone-free method like the copper coil, your body returns to its baseline hormonal state. If the pill was masking a tendency toward weight gain, the gain may appear to coincide with the coil when it is actually related to stopping the pill.

There is also the psychological dimension. If you are worried about weight gain as a side effect, you are more likely to notice small fluctuations and attribute them to the coil. A kilogram of normal daily weight variation (fluid, food, bowel contents) can feel like confirmation of a fear.

Copper coil side effects that are real

The copper coil does have genuine side effects, but weight gain is not among the evidence-based ones.

The main side effects are heavier, longer periods and increased menstrual cramping, particularly in the first 3-6 months after fitting. For most women this settles. For a minority, periods remain heavier than they were before the coil and this becomes a reason for removal.

Some women also report increased PMS-like symptoms (bloating, breast tenderness, mood changes) around menstruation. Whether the copper coil causes this directly or whether heavier periods simply make pre-existing PMS more noticeable is debated. There is no established hormonal mechanism, since the coil is hormone-free, but patient experience is real and should not be dismissed.

What to do if you have gained weight with a copper coil

If you have gained weight since having a copper coil fitted, the coil is unlikely to be the cause, but it is still worth investigating.

A well woman check or blood test panel can rule out thyroid dysfunction, insulin resistance, and hormonal imbalances that might explain the change. These are common, often undiagnosed conditions that can cause gradual weight gain. Catching them early makes them easier to manage.

If you are experiencing other symptoms alongside weight gain (fatigue, hair thinning, mood changes, irregular periods despite the coil), a broader hormonal assessment is particularly worth doing.

If you are unhappy with the copper coil for any reason, whether weight-related or otherwise, you can have it removed at any time. Discuss your options with a gynaecologist. A hormonal coil like the Mirena, the Kyleena, or a different contraceptive method altogether may be a better fit.

The bottom line

The copper coil does not cause weight gain. There is no hormonal pathway for it to do so, and controlled studies have not found an association. If you have gained weight since your copper coil was fitted, the cause is almost certainly elsewhere, and it is worth finding out what it is rather than removing a contraceptive that is otherwise working well.

If you are considering a copper coil and weight gain is a concern, it should not be a factor in your decision. If anything, the copper coil's hormone-free status makes it one of the least likely contraceptives to affect your weight.

More information on copper coil fitting, pricing, and what to expect is on our coil fitting page.