Home pregnancy tests work by detecting the presence of human chorionic gonadotropin (hCG) in a urine sample. There are a few things that can cause a false negative reading, namely the improper use of the test, testing too early, using an expired test, or diluting the urine by drinking too much water in advance.
There are also a few medications that can interfere with the result. Rather than triggering a false negative, they can sometimes return a false positive reading, leading to you believe that you are pregnant when, in fact, you are not.
HCG Medications
Some of the drugs used during in vitro fertilization (IVF) or intrauterine insemination (IUI) can interfere with hCG measurements because they are forms of hCG.
Women unable to ovulate on their own are often prescribed a fertility medication such as Clomid (clomiphene citrate). After completing the five-day course, a "trigger shot" of Pregnyl, Ovidrel, or Novarel may be used to mature eggs and induce ovulation.
Typically, it takes about 10 days for the synthetic hCG in these trigger shots to clear from your blood and urine. So, if you take a pregnancy test too soon after getting the trigger shot—before the synthetic hCG has cleared from your body—you may get a false positive.
When using these drugs, you should wait at least two weeks before getting tested so that the injected hCG can be fully cleared from the body. Most doctors, however, advise against home testing and ask that you come to the office to get a blood-based test. While the blood test also detects hCG, it is far more accurate than a home urine-based test.
HMG Medications
Another type of injectable drug, known as human menopausal gonadotropin (hMG), can be used to aid in ovulation. HMG is made up of two hormones: luteinizing hormone (LH) and follicle-stimulating hormone (FSH). Common hMG medications include Menopur, Pergonal, and Repronex.
When used in the IVF or IUI setting, the LH component can also trigger a false positive result but for different reasons. While an hCG injection triggers a false positive by introducing synthetic hCG into the system, a surge in LH can do the same because the two hormones are so structurally similar.
False Negative Pregnancy Tests
If you've taken a pregnancy test and believe that a negative result is wrong, the best thing to do is wait for at least two days and test again. Often, if you test too early, the hCG levels will be below the threshold of detection of many home pregnancy tests.
HCG levels are typically expected to double every two days if you are pregnant. If you are pregnant and you wait another two days before testing again, the levels should double again, increasing your chance of an accurate reading.
If, on the other hand, you are undergoing IVF or IUI, it is best to follow your doctor's instructions and wait to get an in-office blood hCG test. While having to hold off two weeks can add anxiety to an already emotional process, the risk of a false positive test may be more upsetting than waiting for an accurate reading.
2 Sources
Verywell Family uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
American Society for Reproductive Medicine. Medications for inducing ovulation.
The Fertility Institute. Testing for pregnancy after IVF.
:max_bytes(150000):strip_icc()/Robinnew-59498a045f9b58d58ab8f370.jpg "How Medications Can Affect Pregnancy Test Results (1)")
By Robin Elise Weiss, PhD, MPH
Robin Elise Weiss, PhD, MPH is a professor, author, childbirth and postpartum educator, certified doula, and lactation counselor.
Share Feedback
Was this page helpful?
Thanks for your feedback!
What is your feedback?
FAQs
What medications can affect pregnancy test results? ›
Medications that could affect your test include benzodiazepines, phenothiazine, promethazine and others. Urine contaminated with blood or protein can also trigger a false positive. A laboratory-quality test may be your best option for accurate results.
Can drugs in your system affect a pregnancy test? ›Alcohol and illicit drugs also don't affect pregnancy test results. Other factors that can cause inaccurate results on pregnancy tests may include: Incorrect use of the test. Testing too early.
Can any medications cause a false positive pregnancy test? ›Other medications can also cause false-positive pregnancy tests. They include but aren't limited to: anti-anxiety medications, like diazepam (Valium) or alprazolam (Xanax) antipsychotics, such as clozapine or chlorpromazine.
What can affect the accuracy of a pregnancy test? ›Drinking too much water — or any liquid — can affect a pregnancy test. The hormone hCG is more concentrated in your urine first thing in the morning. If you haven't missed your period yet, your hCG level may not be high enough to be detected in more diluted urine.
What causes false pregnancy test results? ›A test will only show a false positive if you have hCG in your system for another reason such as you were recently pregnant, are taking fertility medications containing hCG, or if you have a medical condition, like some rare ovarian cysts.
What can affect hCG levels in urine? ›Factors that could affect results
In addition to testing too early, the following factors can cause a false negative with a urine HCG test: drinking lots of water so that the urine is very diluted. getting too much or too little urine on the test strip. testing with urine late in the day when it may be weaker.
Certain medications, including those that contain hCG, can interfere with hCG blood test results. These include fertility drugs such as Profasi, Pregnyl, and Pergonal. Smoking marijuana can also result in elevated hCG levels. Test results can also be influenced by the presence of germ cell tumors.
Can ibuprofen affect pregnancy test? ›Most medicines should not affect the results of a home pregnancy test. This includes over-the-counter and prescription medicines such as birth control and antibiotics. Also, alcohol and illegal drugs do not affect pregnancy test results.
What can cause 2 false-positive pregnancy test? ›Home pregnancy tests can be up to 99% accurate. However, in some instances, they may produce a false-positive result. Incorrect test usage, previous abortions and miscarriages, and some medications may lead to a false-positive pregnancy test result. People should always see their doctor after a positive pregnancy test.
What is the most common cause of false-positive hCG results? ›Most of these false-positive results are due to interference by non-human chorionic gonadotropin substances (especially human luteinizing hormone and anti-animal immunoglobulin antibodies) and the detection of pituitary human chorionic gonadotropin.
What can cause 5 false-positive pregnancy test? ›
Some medications may create a false positive pregnancy test result as well. These include some anticonvulsants, anti-anxiety drugs, antihistamines, diuretics, chemotherapy medications, antipsychotics, drugs that treat Parkinson's disease, and methadone.
Can too much pee on a pregnancy test make it negative? ›If you have too little, (if you took the test too early or diluted your urine), it won't be detected. If you have too much, (if you took the test too late), the test strip may not be able to bond to any of the molecules, possibly showing a negative result.
Is it possible to be pregnant but test negative? ›Is it possible to be pregnant and get a negative pregnancy test result? Yes, it is possible. Getting a negative result doesn't mean you're not pregnant, it may just mean your hCG levels are not high enough for the test to detect the hormone in your urine.
Why is the line so faint on my pregnancy test? ›The strength of the positive test line depends on how much hCG is in your urine. If the line is faint, it usually means that the hCG level is low. One reason why hCG levels may be low could be because you're still very early into your pregnancy.
Can you be 5 weeks pregnant and test negative? ›Yes, it is possible. Getting a negative result doesn't mean you're not pregnant, it may just mean your hCG levels are not high enough for the test to detect the hormone in your urine.
Why am I getting negative pregnancy tests but no period? ›The most common reason for a late period and a negative pregnancy test is that your period is simply delayed and you're not pregnant. Having one or two irregular cycles a year is not unusual and does not mean there is something wrong. Reasons your period might be late include: Breastfeeding.
How rare is false-positive pregnancy? ›A false-positive test result only happens less than 1% of the time, but when it does, it can make the following days or weeks confusing before you realize you're not actually pregnant.
How often are pregnancy tests wrong false negative? ›“The false negative rate, if done appropriately, is less than 1%.” If someone waits until the appropriate point in their menstrual cycle and ensures that their urine is concentrated enough at the time of testing, then it's highly unlikely that an at-home pregnancy test will provide incorrect results, he explains.
Can a pregnancy test be positive one day and negative the next? ›This is because hCG levels rise rapidly in the first few days after implantation. It's also possible to get a positive test result followed by a negative result. If you use two different pregnancy tests, this could be the result of varying test sensitivity. Wait a few days and test again.
How much hCG is needed for a positive urine test? ›Pregnancy blood tests can detect hCG hormone levels as low as 5 to 10 mIU/mL. Urine tests. At-home urine tests require higher levels of hCG to detect a pregnancy, typically at least 20 mIU/mL.
What not to do before taking a pregnancy test? ›
Don't drink too much water, or any liquid, before taking a pregnancy test. Excess fluids can impact the accuracy of the test results, so if your urine is diluted or pale yellow, hold off on taking a test. Diluted urine tends to also have diluted hCG levels which can skew the test results.
Can dehydration affect hCG levels in urine? ›Although not common, dehydration can cause spotting in pregnancy. It's believed some women experience spotting when dehydrated, as their hCG levels temporarily stop increasing, or dip. Once re-hydration is reached, hCG levels level out and spotting may stop.
Can your hCG be low and still be pregnant? ›When hCG Trends Are Abnormal. A low hCG level can mean your pregnancy date was miscalculated and you're not as far along as you had thought. Further testing would be needed to determine the cause, which may or may not include a miscarriage, a blighted ovum, or an ectopic pregnancy.
Can stress affect your hCG levels? ›In conclusion, stress-related hormones affect placental HCG secretion in vitro. The involvement of these factors in impairing early pregnancy development is suggested.
Can medication affect hCG levels? ›If you're taking a medication that contains or affects hCG production, it's possible that you could receive a false pregnancy test result. This means you could receive a positive test without actually being pregnant, or (more rarely) a negative test when you are pregnant.
Can Benadryl cause a false negative pregnancy test? ›Some diuretics and antihistamines can cause false negatives.
Can a UTI cause a false positive pregnancy test? ›Serious urinary tract infections (with high levels of WBC, RBC and nitrite) can occasionally cause a false positive pregnancy test result.
Can Clearblue show false positive? ›All Clearblue® pregnancy tests are over 99% accurate from the day you expect your period. False positives can occur if you're taking fertility medications that contain hCG, if you have a rare medical condition (such as an ovarian cyst) or if you've recently had a birth, miscarriage or termination.
What infections can cause a false positive pregnancy test? ›There are also some medical conditions that can cause false pregnancy positives. These conditions can vary, but some of the more common ones include urinary tract infections, ovarian cysts, and kidney diseases.
Is it better to dip a pregnancy test or pee on it? ›Should I dip my home pregnancy test in urine, or pee on it? Most tests allow you to either place the absorbent tip in your urine stream for (usually) five seconds or dip the tip in a collected urine sample for five to 20 seconds. Accuracy is not dependent on the method as long as you follow the instructions.
Is it better to pee directly on a pregnancy test? ›
Depending on the particular home pregnancy test, you should pee in a collection cup or pee directly onto the pregnancy test stick. Some tests will give you the option to collect your urine either way.
How long should you hold your urine before taking a pregnancy test? ›When possible, try to wait until it's been three hours since your last pee before you take the test. You could also take two pregnancy tests to confirm you get the same result.
Why is my pregnancy test negative but I have all the symptoms? ›If you feel as though you're pregnant but got a negative home pregnancy test result, your symptoms could be down to premenstrual syndrome (PMS) or you may have taken the test too early.
Can stress cause false pregnancy symptoms? ›However, other elements or events can trigger a phantom pregnancy. Physical problems or psychological problems may be involved. The loss of a child, a miscarriage, a voluntary termination of pregnancy, an inability to conceive children, family problems or a period of intense stress can cause such symptoms.
Why do I think I'm pregnant? ›Many people experience what seem to be pregnancy symptoms shortly before their period arrives. This happens because the hormone progesterone rises both during early pregnancy and in the premenstrual period. 1 In short, PMS symptoms and early pregnancy symptoms can sometimes be exactly the same.
How long after a faint positive should I test again? ›So, if you do get a faint line, Kirkham recommends waiting two or three days, then testing again. If it's still faint, she suggests going to your family doctor for a blood test, which can measure the specific amount of beta hCG, to check if the pregnancy is progressing as it should.
Can a faint line still be negative? ›Can a barely visible pregnancy test result be negative? A barely visible pregnancy test result usually can't be negative — because it detected hCG — but it might indicate a false positive or an early pregnancy loss. However, false positive results that are not related to early pregnancy loss are incredibly rare.
Can a very faint line be negative? ›Can faint lines also denote a negative result? In most cases, faint lines result from HCG detection and can denote a true pregnancy, an early pregnancy loss or a false positive pregnancy. However, there are a few instances where faint lines on a pregnancy test can also result in negative results.
What can cause hCG not to show in urine? ›Too much hCG in the urine
If you have too little, (if you took the test too early or diluted your urine), it won't be detected. If you have too much, (if you took the test too late), the test strip may not be able to bond to any of the molecules, possibly showing a negative result.
All Clearblue® pregnancy tests are over 99% accurate from the day you expect your period. False positives can occur if you're taking fertility medications that contain hCG, if you have a rare medical condition (such as an ovarian cyst) or if you've recently had a birth, miscarriage or termination.
Is second morning urine better for pregnancy test? ›
In general, the best time is when you have your first morning pee. However, some pregnancy tests are sensitive enough to detect HCG no matter what time of day you take the test.