Opill 28 Day Side Effects: What to Expect and When to Call Your Doctor

Opill (norgestrel 0.075 mg) is the first FDA-approved over-the-counter birth control pill in the United States. As a progestin-only pill, it has a different side effect profile than combination birth control pills — notably, it does not increase the risk of blood clots, high blood pressure, or stroke the way estrogen-containing pills can.

That said, Opill does have side effects. Most are mild and tend to improve after the first few months. This post covers what to realistically expect, which symptoms are normal, and which ones mean you should call your doctor.

The Most Common Opill Side Effect: Irregular Bleeding

By far the most frequently reported side effect of Opill is changes in your menstrual bleeding pattern. This is true of progestin-only pills in general. Because Opill does not contain estrogen — which helps regulate and schedule bleeding in combination pills — your cycle may become unpredictable, especially in the first 2–3 months.

What you might experience:

Spotting or breakthrough bleeding between periods

Lighter periods than usual

Heavier or more frequent periods in some users

Missed periods or amenorrhea (no period) — about 20% of progestin-only pill users stop having periods, which is not dangerous

In a clinical survey of Opill users, 58% said the bleeding pattern was similar to or better than their previous hormonal birth control method. Irregular bleeding from Opill is not dangerous, but if you experience very heavy bleeding (soaking more than one pad or tampon per hour for 2+ hours), contact your doctor.

Other Common Opill Side Effects

The FDA's approved labeling for Opill lists the following common side effects:

Headaches: Usually mild. If you develop new severe headaches, migraines with aura (visual changes, weakness, difficulty speaking), or recurring migraines, contact your provider — these can indicate increased stroke risk in some people.

Dizziness: Often mild and temporary, particularly when first starting Opill.

Nausea: Taking Opill with food or at bedtime can help. Nausea usually improves after the first few weeks.

Increased appetite: Some users report feeling hungrier than usual. Research does not consistently show significant weight gain with progestin-only pills.

Abdominal pain, cramps, or bloating: Generally mild. Severe or sudden lower abdominal pain — especially one-sided — should be evaluated promptly to rule out an ectopic pregnancy.

Breast tenderness: Typically resolves within the first 1–2 months.

Mood changes: Some users report mild mood effects or low mood. Persistent depression or anxiety should be discussed with a provider.

What Opill Does NOT Do (Compared to Combination Pills)

Because Opill contains no estrogen, it does not carry estrogen-related risks. Specifically, Opill does NOT:

Increase your risk of blood clots (deep vein thrombosis or pulmonary embolism)

Raise blood pressure

Increase stroke risk in people with migraines without aura

Pose the same risks to smokers over 35 that combination pills do

This is a major reason why people with certain medical conditions that make combination pills risky are often good candidates for Opill.

Serious Side Effects: When to Call Your Doctor Right Away

While rare, Opill can cause serious side effects. Seek medical attention immediately if you experience:

Severe or one-sided lower abdominal pain: This can be a sign of ectopic pregnancy, which is a medical emergency. Women who become pregnant while on Opill have an elevated risk of ectopic pregnancy (pregnancy occurring outside the uterus).

Signs of liver problems: Yellowing of the skin or whites of the eyes (jaundice), dark-colored urine, upper right abdominal pain, or extreme fatigue. Though rare, progestins can affect liver function.

Severe allergic reaction: Hives, facial swelling, difficulty breathing, blisters. Opill contains FD&C Yellow No. 5 (tartrazine), which can trigger allergic reactions in some people, including those allergic to aspirin. Stop taking Opill and seek emergency care immediately.

Ovarian cysts: Progestin-only pills can be associated with delayed follicular atresia and ovarian cysts. These are usually benign, but in rare cases they may twist or rupture, requiring medical intervention. Severe pelvic pain warrants evaluation.

New or worsening migraines: Particularly migraine with aura (visual changes, muscle weakness, difficulty speaking). While Opill is safer than combination pills for migraine, new neurological symptoms should be evaluated.

What If You're Already Pregnant?

If you miss two periods in a row while on Opill (or miss one period but have also missed pill doses), take a pregnancy test. If you think you may be pregnant, stop taking Opill and contact your provider. Opill is not for use during pregnancy.

How Long Do Side Effects Last?

Most of Opill's common side effects — irregular bleeding, nausea, breast tenderness, mild headaches — tend to improve significantly after 2–3 months as your body adjusts to the hormone. If bothersome side effects persist beyond 3 months or are severe from the start, talk to a healthcare provider about whether Opill is right for you or whether a different contraceptive method might suit you better.

If you're considering a switch, see our comparison of alternatives to Opill.