False positive pregnancy tests are uncommon, but they do happen. The most frequent causes include fertility medications that contain the pregnancy hormone, reading the test outside its time window, and very early pregnancies that end before they’re ever noticed. Less commonly, certain medical conditions and other medications can trigger a positive result when you’re not pregnant.
Fertility Medications Containing hCG
Home pregnancy tests work by detecting human chorionic gonadotropin (hCG), a hormone produced during pregnancy. Some fertility treatments involve injecting this exact hormone to trigger ovulation or support early pregnancy. Brand names include Pregnyl, Profasi, Novarel, and Ovidrel. If you take a pregnancy test while these medications are still in your system, the test is picking up the injected hormone rather than a pregnancy.
The timing varies depending on the dose and the specific medication, but fertility clinics typically advise waiting a set number of days after your last injection before testing at home. Testing too early is one of the most common reasons people undergoing fertility treatment see a positive that doesn’t reflect an actual pregnancy.
Evaporation Lines
This is probably the single most common source of confusion. Every home pregnancy test has a reaction window, usually two to five minutes depending on the brand. If you check the test after that window closes, urine drying on the test strip can leave a faint, colorless line where the positive result would normally appear. This is called an evaporation line, and it’s easy to mistake for a faint positive, especially if you’re hoping to see one.
To avoid this, read your result within the exact timeframe listed in the instructions and then discard the test. Going back to check it an hour later, or pulling it out of the trash the next morning, significantly raises the chance of seeing a misleading line. A true positive typically shows clear color (pink or blue, depending on the brand) within the stated time window.
Chemical Pregnancies
A chemical pregnancy is a very early miscarriage that happens shortly after a fertilized egg implants. It produces enough hCG to trigger a positive test, but the pregnancy ends before it can be seen on an ultrasound. This is technically not a false positive. You were pregnant, just very briefly.
About 25% of all pregnancies end within the first 20 weeks, and roughly 80% of those losses happen early, according to Cleveland Clinic data. Many chemical pregnancies occur right around the time your period is expected, so without a test, most people would never know they were pregnant. They’d simply experience what seems like a normal or slightly late period. Today’s highly sensitive tests can detect pregnancy earlier than ever, which means they also catch more of these very short-lived pregnancies.
Certain Medications
Beyond fertility drugs, several other types of medication have been linked to false positive pregnancy tests. These don’t contain hCG, but their chemical structures can interfere with the antibodies used in test strips. The list includes:
- Antipsychotic medications used for conditions like schizophrenia, including chlorpromazine, perphenazine, and thioridazine
- Anti-nausea drugs such as promethazine and prochlorperazine
- The anticonvulsant carbamazepine, prescribed for epilepsy, nerve pain, and bipolar disorder
- Some anti-anxiety medications including prochlorperazine and trifluoperazine
If you’re taking any of these and get an unexpected positive result, a blood test at your doctor’s office can measure your exact hCG level and confirm whether pregnancy is actually the cause.
Expired or Damaged Tests
Pregnancy tests contain chemical reagents that degrade over time. An expired test, or one that’s been stored in a hot bathroom, car glove compartment, or humid environment, may not perform the way it’s supposed to. The degradation can affect the test’s sensitivity and reliability, potentially producing an inaccurate reading in either direction.
Always check the expiration date on the box before use and store tests in a cool, dry place. If you get a surprising result from a test that’s been sitting in a drawer for a couple of years, it’s worth retesting with a fresh one.
Medical Conditions That Raise hCG
Certain health conditions cause your body to produce hCG even when you’re not pregnant. A molar pregnancy is one example. This occurs when abnormal tissue grows in the uterus instead of a viable embryo. Complete molar pregnancies often produce extremely high hCG levels, with about half exceeding 100,000 mIU/mL, well above normal early pregnancy ranges. Partial molar pregnancies tend to produce lower levels, but still enough to trigger a positive test.
Rarely, some cancers produce hCG. Tumors of the liver, lung, pancreas, stomach, and certain germ cell tumors (including testicular cancer) can release this hormone. In these cases, the cancerous cells essentially mimic the placental cells that normally produce hCG during pregnancy. This is uncommon, but it’s one reason an unexplained positive test in someone who couldn’t be pregnant warrants medical follow-up.
Marijuana use has also been associated with elevated hCG levels, though this is less well understood.
Menopause and Perimenopause
As estrogen levels drop during menopause, the pituitary gland can start producing small amounts of hCG. This isn’t related to pregnancy at all. It’s a byproduct of the same hormonal shifts that cause hot flashes and irregular periods. Among postmenopausal individuals aged 55 and older, up to 8% may have hCG levels high enough to trigger a positive result on a standard test. For this reason, the American College of Obstetricians and Gynecologists has recommended using a higher hCG cutoff (14 international units/L instead of the standard 5) when evaluating test results in this age group.
If you’re in your late 40s or older and get an unexpected positive, this hormonal shift is a real possibility worth discussing with your provider.
How to Rule Out a False Positive
If you get a positive result you weren’t expecting, the simplest first step is to take a second test from a different brand, using your first morning urine (which has the highest concentration of hCG). Make sure you read the result within the time window printed on the instructions. If the second test is also positive, a blood draw can measure your exact hCG level and, with repeat testing a couple of days later, show whether that level is rising the way it would in a viable pregnancy.
True false positives, where no pregnancy of any kind exists, are rare. In most cases, a positive test reflects real hCG in your system. The question is where it’s coming from.