From the Guidelines

Bleeding is a normal and common side effect with Intrauterine Device (IUD) use, especially during the first 3-6 months after insertion 1.

Copper IUD (Cu-IUD): Unscheduled spotting or light bleeding, as well as heavy or prolonged bleeding, is common during the first 3-6 months of use, but generally decreases with continued use 1.
Levonorgestrel IUD (LNG-IUD): Unscheduled spotting or light bleeding is expected during the first 3-6 months of use, but heavy or prolonged bleeding is uncommon 1.

Nonsteroidal anti-inflammatory drugs (NSAIDs): Can be used for short-term treatment (5-7 days) of bleeding irregularities with Cu-IUD use 1.
Alternative contraceptive methods: Should be considered if bleeding persists and is unacceptable to the woman 1.

Underlying gynecological problems: Should be ruled out if heavy or prolonged bleeding occurs, especially in women who have been using the IUD for a few months or longer 1.
Counseling: Enhanced counseling about expected bleeding patterns and reassurance that bleeding irregularities are generally not harmful can reduce method discontinuation 1.

From the Research

Bleeding problems are a common side effect of IUDs and can be an important medical reason for discontinuation of use 2
The pathogenesis of IUD-associated bleeding problems is not yet fully understood, and a standard universally acceptable therapy is not yet available 2
Hormone-releasing devices, such as the levonorgestrel-releasing intrauterine system (LNG-IUS), can reduce the amount of bleeding significantly, but may cause a post-insertion phase of irregular spotting 2, 3
Copper-containing IUDs can cause increased uterine bleeding and pain, which may decrease over time 4
Bleeding irregularities, such as intermenstrual spotting or heavy or prolonged menstrual bleeding, are common among copper-containing IUD users and are one of the leading reasons for method discontinuation 5

Nonsteroidal anti-inflammatory drugs (NSAIDs) may be effective treatments for bleeding irregularities associated with copper-containing IUD use 5
Antifibrinolytic agents and antidiuretics have also been studied as possible treatments, but their safety has not been well documented 5
NSAIDs and antifibrinolytics may also prevent bleeding irregularities among new copper-containing IUD users, although preventive NSAID use does not impact IUD continuation 5
The FibroPlant levonorgestrel IUS has been shown to be effective in significantly reducing the amount of menstrual blood loss in women with menorrhagia, with a low incidence of hormonal side-effects and no cases of amenorrhea 3

Uterine perforation caused by modern copper IUDs and the levonorgestrel-releasing intrauterine system (LNG-IUS) can occur, but symptoms are mostly mild and approximately 30% of women are asymptomatic 6
Surgical findings are mainly minimal, with no visceral complications found in one study, but adhesions and pregnancies seem to be more common among women using copper IUDs 6