Does a Copper (Cu) Intrauterine Device (IUD) prevent menses or just pregnancy?

Copper IUD Does NOT Prevent Menses—It Only Prevents Pregnancy

You are correct: the copper IUD (Cu-IUD) prevents pregnancy but does NOT prevent menstruation. In fact, the copper IUD typically increases menstrual bleeding rather than stopping it 1.

Mechanism of Action

• The copper IUD works primarily by preventing fertilization, not by stopping ovulation or menstruation 2, 3.
• Copper ions create a toxic environment for sperm and ova, preventing sperm from fertilizing eggs through prefertilization mechanisms 1.
• Women using copper IUDs continue to ovulate normally and have regular menstrual cycles 2.

Effect on Menstrual Bleeding

The main side effect of the copper IUD is actually increased menstrual bleeding:

• Copper IUDs increase menstrual blood loss by approximately 50% 2.
• This increased bleeding may continue even with long-term use 1.
• Women should be counseled that heavier periods are expected with copper IUD use 1.

Contrast with Hormonal IUDs

This is an important distinction from levonorgestrel-releasing IUDs (LNG-IUDs), which work differently:

• Hormonal IUDs (LNG-IUDs) substantially reduce menstrual blood loss and can cause oligomenorrhea (light periods) or amenorrhea (no periods) 2, 1.
• The LNG-IUD releases 14-20 mcg of levonorgestrel per 24 hours, which thins the endometrial lining and can suppress menstruation 1.

Clinical Counseling Point

When counseling patients, emphasize that:

• The copper IUD provides highly effective contraception (pregnancy rates of 1.0-1.8% over 3-9 years) 3.
• Patients will continue having periods—and likely heavier ones 2, 1.
• If a patient desires amenorrhea or lighter periods, a hormonal IUD would be the appropriate choice instead 2, 1.