The primary medication used to treat ectopic pregnancy is methotrexate, given as an injection. Originally developed as a cancer drug, methotrexate works by blocking the cells of the early pregnancy from dividing and growing, which causes the ectopic tissue to break down and be reabsorbed by the body. It’s a well-established alternative to surgery for many patients, with an overall success rate around 87% in appropriate candidates.
How Methotrexate Works
Methotrexate targets rapidly dividing cells by interfering with how they use folate (a B vitamin) to build DNA. The cells that form the early placenta divide extremely fast, making them particularly vulnerable to this drug. Once those cells stop multiplying, the ectopic pregnancy stops growing and gradually resolves on its own. The medication is given as an intramuscular injection, typically in the hip or thigh.
Who Qualifies for Medication Instead of Surgery
Not everyone with an ectopic pregnancy can be treated with methotrexate. It works best under a specific set of conditions, and your doctor will run blood tests and an ultrasound to determine if you’re a good candidate.
You’re generally a strong candidate if:
- Your hCG level is below 5,000 mIU/mL. This pregnancy hormone level is the clearest predictor of success. Below 1,500, success rates are highest.
- The ectopic mass is smaller than 3.5 cm.
- There’s no detectable heartbeat in the ectopic pregnancy on ultrasound.
- The fallopian tube hasn’t ruptured and you’re hemodynamically stable (not showing signs of internal bleeding).
As hCG levels climb above 5,000, success rates drop. In one study, women with levels between 2,500 and 3,500 had a 75% success rate, dropping to 65% when levels exceeded 4,500. The presence of a heartbeat on ultrasound also raises the risk of treatment failure significantly.
Methotrexate is not an option if you have kidney disease, liver disease, active lung disease, a blood disorder, an immune deficiency, peptic ulcer disease, or a known allergy to the drug. You also cannot receive it if you’re breastfeeding or if an intrauterine pregnancy hasn’t been ruled out.
Single-Dose vs. Multi-Dose Protocols
There are two main approaches. The single-dose protocol is the more common starting point: one injection calculated at 50 mg per square meter of body surface area. Despite the name, some patients end up needing a second injection if their hormone levels don’t drop enough.
The multi-dose protocol involves smaller, alternating injections over several days, paired with a rescue medication called leucovorin that protects healthy cells. This approach tends to be used for higher hCG levels or more complex cases. One guideline suggests single-dose treatment when initial hCG is below 1,500 and multi-dose when it’s below 3,000.
What Happens After the Injection
Methotrexate isn’t instant. After the injection, your doctor will check your hCG blood levels on day 4 and day 7. The key milestone: hCG needs to drop by at least 15% between those two draws. If it does, the treatment is considered on track, and you’ll continue with weekly blood draws until hCG falls to undetectable levels. This process can take several weeks.
If hCG hasn’t dropped enough by day 7, a second dose of methotrexate may be recommended. About 13% of women treated with methotrexate ultimately need surgery (laparoscopic removal of the affected tube) because the medication doesn’t fully resolve the pregnancy.
Side Effects to Expect
The most common side effects are nausea, abdominal pain, and fatigue. Mouth sores (ulcerative stomatitis) are also frequently reported. Some women experience chills, mild fever, or dizziness. These effects are generally temporary and mild at the doses used for ectopic pregnancy.
One important note: mild to moderate abdominal pain in the days after the injection is common and doesn’t necessarily mean something has gone wrong. This “separation pain” happens as the ectopic tissue breaks down. However, sudden and severe abdominal or pelvic pain, shoulder pain, or feeling faint or weak are signs of a possible tubal rupture, which requires emergency care immediately.
What to Avoid During Treatment
While your body processes the methotrexate, certain substances can interfere with treatment or worsen side effects:
- Folic acid and prenatal vitamins. Since methotrexate works by blocking folate, taking folic acid supplements counteracts the drug. Stop prenatal vitamins until your doctor says otherwise.
- Alcohol. Methotrexate is processed by the liver, and alcohol adds strain. Avoid it entirely during treatment.
- NSAIDs like ibuprofen. These can interact with how your body clears methotrexate, raising the risk of toxicity.
- Certain antibiotics. Specifically, trimethoprim-sulfa combinations (such as Bactrim) should not be taken alongside methotrexate.
You’ll also need to avoid sun exposure, as methotrexate can increase skin sensitivity. Sexual intercourse and strenuous exercise are typically off-limits during treatment to reduce the risk of tubal rupture.
Getting Pregnant Again After Treatment
Most guidelines recommend waiting at least three months after methotrexate before trying to conceive. This allows the drug to fully clear your system and your folate levels to recover, since folate is critical for early fetal development. Some sources suggest waiting a full six months for an extra margin of safety.
Research from the Canadian Family Physician found that pregnancies conceived shortly after methotrexate treatment for ectopic pregnancy generally had favorable outcomes similar to those conceived after six months. That said, if conception happens within three months of treatment, it’s not automatically cause for termination. Additional fetal monitoring through targeted anatomy scans is recommended in those cases. Methotrexate treatment for ectopic pregnancy does not appear to reduce your chances of a successful pregnancy in the future.