Breakthrough bleeding, or spotting between periods, is most commonly caused by hormonal contraceptives, but it can also result from infections, medications, ovulation, early pregnancy, or lifestyle factors like smoking. The type and timing of your bleeding often points directly to the cause.
How Hormonal Contraceptives Cause Spotting
The most common reason for breakthrough bleeding is hormonal birth control. Whether you use the pill, a hormonal IUD, an implant, or an injection, the mechanism is similar: the hormones alter the lining of your uterus in ways that can make it structurally fragile.
With combined birth control pills, the estrogen dose is deliberately kept low to reduce side effects. But lower estrogen means less support for the uterine lining. The progestin in the pill causes the lining to thin and shrink over time, and this thinned-out tissue can shed unpredictably in small patches. The result is light spotting or bleeding at random points in your cycle. This is the single most frequent cause of breakthrough bleeding in pill users.
With progestin-only methods (the mini-pill, the implant, the hormonal IUD, or the injection), the pattern is even more pronounced. Continuous progestin exposure suppresses the uterine lining so aggressively that it becomes atrophic, meaning very thin with fragile blood vessels. Small areas of this weakened lining detach on their own, producing spotting that has nothing to do with a normal menstrual cycle.
Timeline for IUDs and Implants
If you recently had a hormonal IUD placed, irregular bleeding and cramping are normal for the first three to six months. It takes that long for the progestin to fully suppress your uterine lining. Over time, bleeding typically decreases and many women eventually have very light or absent periods.
The implant (Nexplanon) is a different story. About 78% of users experience some form of irregular bleeding during any three-month window. In clinical trials, roughly a third of women had infrequent bleeding, about one in five stopped bleeding entirely, and 18% had prolonged bleeding episodes. Unlike the IUD, these patterns don’t settle into a predictable rhythm. Bleeding can remain random and unpredictable for the full three years the implant is in place.
Missing Pills or Inconsistent Use
Breakthrough bleeding is your body’s signal that hormone levels have dipped. Missing a pill, taking it at irregular times, or having a stomach illness that prevents absorption can all trigger spotting. Even among consistent users, the first few cycles on a new pill commonly involve breakthrough bleeding as your body adjusts. This typically resolves within three to six months.
Smoking and Estrogen Levels
Smoking speeds up how quickly your body breaks down estrogen, effectively lowering the hormone levels your birth control delivers. This has a measurable effect on breakthrough bleeding. Smokers are, on average, 47% more likely to experience spotting than nonsmokers over six cycles of pill use. The more you smoke, the worse it gets: women who smoked 16 or more cigarettes per day were nearly three times as likely to have breakthrough bleeding by the sixth cycle compared to nonsmokers. If you smoke and use hormonal contraception, this may be a significant contributor to your spotting.
Medications That Interfere With Birth Control
Certain medications can reduce the effectiveness of hormonal contraceptives by increasing how fast your liver processes the hormones. When hormone levels drop below the threshold needed to keep your uterine lining stable, spotting follows. Common culprits include some anti-seizure medications, certain antibiotics (particularly rifampin), some HIV medications, and the herbal supplement St. John’s wort. If you started a new medication and noticed breakthrough bleeding soon after, the two may be connected.
Infections and STIs
Bleeding between periods can be a symptom of a sexually transmitted infection, particularly chlamydia and gonorrhea. Chlamydia can cause bleeding between periods even when no other symptoms are present. Gonorrhea can cause heavy menstrual bleeding or intermenstrual spotting. Both infections inflame the cervix, which makes the tissue more likely to bleed. Since many STIs produce few or no other symptoms, unexpected bleeding that isn’t explained by contraceptive use is worth getting tested for.
Ovulation Spotting
Some women experience light spotting around the middle of their cycle, right when they ovulate. This happens because estrogen levels dip briefly after the egg is released, and that temporary hormone drop can cause a small amount of uterine lining to shed. Ovulation spotting typically lasts just a day or two and is very light. If you’re not on hormonal birth control and notice consistent mid-cycle spotting, this is one of the most benign explanations.
Implantation Bleeding in Early Pregnancy
If there’s any chance you could be pregnant, very light bleeding about 10 to 14 days after ovulation could be implantation bleeding. This occurs when a fertilized egg attaches to the uterine wall. It looks different from a period or typical breakthrough bleeding in a few key ways: it’s usually pink or brown (not bright red), extremely light (more like discharge than a flow), and it shouldn’t soak through a pad. It resolves on its own within about two days. If your bleeding is heavy, bright red, or contains clots, it’s likely something else.
What You Can Do About It
The right approach depends on the cause. If you’re in the first few months of a new hormonal contraceptive, the standard advice is to wait it out for at least three cycles, since most spotting resolves as your body adjusts. Consistency matters: take your pill at the same time every day, and don’t skip doses.
For active bleeding episodes on combined hormonal contraceptives, short-term use of an anti-inflammatory like ibuprofen can help. A clinical protocol used by gynecologists is ibuprofen taken every eight hours for two to three days to stop an acute episode. If spotting persists beyond three to six months on any method, switching to a different formulation or type of contraceptive often helps.
If you smoke, reducing or quitting can meaningfully improve cycle control on the pill. And if your breakthrough bleeding started after beginning a new medication, your prescriber may be able to adjust your contraceptive method or dosage to compensate for the interaction.