does weed affect pregnancy tests

Pregnancy Test Guide

Medically reviewed by Leigh Ann Anderson, PharmD. Last updated on Jul 1, 2020.

There are two different types of pregnancy tests: those that check the blood and those that check the urine. The pregnancy blood (serum) test must be performed at a doctor’s office or clinic, but the urine test can be performed at home or in a clinic.

Many woman like the convenience and privacy of using an at home urine pregnancy test to initially determine if they are pregnant or not. Home pregnancy tests are very accurate (if used properly), inexpensive and easily available at the pharmacy. Most only take about 10 minutes to see the results.

If a pregnancy test is found to be positive, or if it is negative but the woman still suspects she might be pregnant, she should contact her health care provider.

What early pregnancy symptoms or pregnancy signs may occur?

The first sign of pregnancy that many women experience is a missed menstrual cycle (their period). Other early symptoms of pregnancy or signs of pregnancy might be:

  • nausea and vomiting (or morning sickness, which can really happen at any time of the day or night)
  • tender or swollen breasts
  • increased urination, especially at night
  • fatigue and tiredness
  • food distastes or food cravings

How do pregnancy tests work and how are they be used?

All pregnancy tests work by detecting the presence of human chorionic gonadotropoin (hCG), the pregnancy hormone.

Both urine and blood pregnancy tests detect the presence of the hormone human chorionic gonadotropin (hCG). The hCG hormone is usually only present in blood or urine if a woman is pregnant.

When an egg fertilized with sperm is implanted in the uterus of the woman the hCG hormone is then produced. The egg usually implants into the wall of the uterus about six days after fertilization, but in about 10% of women implantation may not occur until after the first day of the missed period. The levels of hCG rise in the body early in pregnancy after implantation occurs.

How accurate are home pregnancy tests?

While many early detection pregnancy tests claim to be 99% accurate even one day after a missed period, results can be variable.

  • In up to 10% of women, implantation may not occur until after the first day of the missed period, in which case hormone levels of hCG may not be high enough to be detected by the test.
  • However, research shows that most home pregnancy tests can detect hCG accurately one week after a missed period.
  • Also, testing in the morning the first time you urinate may boost the amount of hCG in the sample and may give you a more accurate result.

A quantitative blood pregnancy test done at the doctor’s office (also known as the beta hCG test) can detect low levels of hCG and measure the actual quantity of hCG in your body. This test may be the most accurate option if a woman needs a pregnancy test very early. Women should contact their physician if they prefer the beta hCG blood test.

If a negative pregnancy result occurs with a home urine test, the test should be repeated in a few days to a week to confirm the negative result. Women with positive pregnancy tests should contact their doctors for an appointment to discuss next steps.

Before a home pregnancy test is purchased, the expiration date should be checked on the outside of the packaging. If the expiration date is passed, do not buy or use the pregnancy test.

Check the expiration date, read the instructions, and follow the specific directions for each home pregnancy test package. Store unopened tests in a cool, dry place.

While home pregnancy tests work in the same way by detecting hCG in the urine, the specific directions for use may vary from test to test. Be sure to read and follow the instructions exactly.

How to read the results on your home pregnancy test

Some tests instruct the user to hold the test stick in the stream of urine, while others involve dipping the stick or pregnancy test strips into a cup of collected urine. It is important to wait the correct number of minutes instructed on the package before the results are read.

Most urine pregnancy tests have a “control” window and another window that is the “results” window. When this line or other symbol appears in the control window it ensures that the test is working properly. If a control window does not show a line or other symbol as indicated by the package instructions, then the test is not working properly. A new pregnancy test should used the next morning.

  • If the control window is working properly, and a line, plus sign, or other symbol as directed by the package instructions appears in the results window, this means the test is positive and the woman is pregnant. For positive results, the woman should contact her physician to make an appointment as soon as possible to start prenatal care.
  • If no symbol appears in the window as directed by the instructions, then the results are most likely negative. However, it is best to confirm the results of a negative test by repeating it in a few days.
  • A faint symbol on the pregnancy test window is usually still positive; it may mean that the levels of hCG in the blood are are still quite low. If a woman is concerned about a faint line on a pregnancy test, it is best to wait a few days and repeat the test, or contact a physician for a confirmatory blood test.

Some digital pregnancy tests now have a digital display window that will report the results in words, such as “pregnant” or “not pregnant”. Digital pregnancy tests may not have a control window, but may show a flashing symbol in the window prior to the result.

Most home pregnancy tests come with a toll-free number to call if the woman has questions.

Where can I get a home pregnancy test and how much will it cost?

Home pregnancy tests are readily available without a prescription and most are very affordable.

  • Home pregnancy tests can be bought without prescriptions at most pharmacies, grocery stores and larger retail chains.
  • You can also buy a pregnancy test over the Internet, but be cautious and buy from a reputable online retailer and always check the expiration date on the outside of the package once the test is received.
  • If the expiration date has passed, do not open the test and return it for a refund.

Brand name home pregnancy tests are available in addition to the less expensive “store brands”. More common brand names of home pregnancy tests include:

  • AccuClear Pregnancy Test
  • Answer Pregnancy Test
  • Clearblue Rapid Pregnancy Test
  • Clearblue Digital Pregnancy Test
  • EPT Pregnancy Test
  • First Response Rapid Results Pregnancy Test
  • Fact Plus Pregnancy Test

Many packages may also contain more than one test, which drive up the costs. On average, home pregnancy tests cost between $5 and $25 depending upon the brand and contents.

Some pregnancy tests can be found for a dollar at popular deep discount stores, and lower-cost “store brands” are just as effective. If you use insurance for your pregnancy test in a doctor’s office or clinic, it may be more expensive than at-home tests.

Where can I get a free pregnancy test?

You may be able to get a free pregnancy test at certain health centers in your community. You might want to call your county health clinic or local Planned Parenthood. Also, ask your nurse or doctor for recommendations.

Which pregnancy test is best?

There is no one answer to this question. All home pregnancy tests should give accurate results if not expired and the directions are followed closely. Many home tests claim to be 99% accurate on the first day of the missed period, but some studies refute this claim.

In one study, researchers compared six home pregnancy tests.

  • They found that the hCG sensitivity of the First Response manual and digital pregnancy tests was 5.5 mlU/mL, while the sensitivity of the EPT and Clear Blue brand was 22 mlU/mL.
  • According to the authors, both First Response tests detected 97% of 120 pregnancies on the day of the missed period.
  • The EPT manual and digital devices detected 54% and 67% of pregnancies, respectively, and the Clear Blue manual and digital devices detected 64% and 54% of pregnancies, respectively, on the day of the missed period. However, other studies have found a greater than 90% accuracy for the ClearBlue tests.
  • Ultimately, following the package instructions and waiting at least a week after the first day of your missed period will give you the most accurate results for all tests. If you receive a negative pregnancy test, it’s always best to test again in a few days to confirm the results.

What is a false positive pregnancy test or a false negative pregnancy test?

A false positive is when the results of the pregnancy test indicate that the woman is pregnant, but in actuality she is not. A false negative pregnancy test is when the results of the test indicate that the woman is not pregnant, but she actually is pregnant. A false-negative is much more likely to occur than a false-positive.

What can cause a false positive pregnancy test?

In rare circumstances, the hCG hormone may be present in the body when a woman is not pregnant and may lead to a pregnancy test false positive result.

Some infertility medications (medications that are used when a woman is having trouble getting pregnant) may cause a false-positive because they contain hCG. Other circumstances that can lead to a false positive include:

  • ovarian cysts
  • recent pregnancies
  • pregnancy loss soon after a fertilized egg implanted (biochemical pregnancy)
  • an ectopic pregnancy
  • a molar pregnancy
  • menopause

What can cause a false negative pregnancy test?

Reasons for a false negative pregnancy test may include:

  • performing the test too early before adequate hCG hormone levels rise
  • timing the test wrong (checking on the results too early)
  • using a dilute urine

To help avoid false negative results, wait for one week after a missed period to use the pregnancy test, use a timer or stopwatch to increase pregnancy test accuracy, and use the first urine of the morning for the test, when the concentration of hCG is at its highest level.

If you continue to get negative test results, but you think you might be pregnant or your period does not start, contact your doctor. There are several other medical conditions that may lead to loss of a period, such as heavy exercise or thyroid problems.

Can medicine or alcohol interfere with the results of a home pregnancy test?

  • Most medications, including birth control pills and antibiotics, do not interfere with pregnancy test results.
  • Alcohol and illegal drugs, such as marijuana, cocaine or heroin may not interfere with the results of a pregnancy test, but these substances should not be used if a woman is trying to conceive, is pregnant or is sexually active without a reliable form of birth control.

Learn More: See the Female Infertility Guide


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  2. Mayo Clinic Staff. Getting Pregnant. Home pregnancy tests: Can you trust the results? Accessed July 1, 2020 at
  3. Johnson S, Cushion M, Bond S, Godbert S, Pike J. Comparison of analytical sensitivity and women’s interpretation of home pregnancy tests. Clin Chem Lab Med. 2015;53(3):391-402. Accessed July 1, 2020 at doi:10.1515/cclm-2014-0643.
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Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

A guide to pregnancy tests. Information includes: types of tests, how they work, effectiveness, common brands and costs.

More pregnant women are using marijuana. We don’t know if that’s safe.

And cannabis dispensaries are marketing their products to pregnant women for morning sickness.

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In a California study, the percentage of pregnant women who screened positive for marijuana use by self-report and/or a positive toxicology test increased between 2009 and 2016, from 4 percent to 7 percent. Getty Images/EyeEm

Soon after Amy Smith* started thinking about having a baby a few years ago, she wondered what she’d do about her marijuana habit.

Smith had deployed twice with the US Army, and had returned from Iraq with severe post-traumatic stress disorder. At one point, her doctors at the VA had her taking 22 pills to help her sleep and quell her depression and anxiety.

Then she discovered marijuana. Smith went off all the prescription medication and began self-medicating by smoking cannabis. “It was amazing — how it helped me get out of bed. I wasn’t terrified of being at the grocery store anymore. I wasn’t on the verge of losing my mind.” (A resident of Utah, the drug only became legal for medical use last November.)

In 2014, Smith became pregnant with her first child. And after Googling studies about the risks, “dancing around the topic” with her doctor, and having many long and difficult discussions with her husband, she decided to use marijuana 4 to 5 times per week while pregnant and while breastfeeding.

“When my anxiety showed up when I was pregnant, I knew what I was in for,” she said. “I could pile up the medications [and] eventually end up in hospital. I chose marijuana instead.”

The marijuana landscape is rapidly changing in the US. Weed has been legalized in 32 states for medical purposes, in 10 states plus DC for recreational use, and cannabis is being marketed directly to pregnant women for morning sickness. And now more and more women are grappling with the question Smith faced: whether to use while pregnant.

The American College of Obstetricians and Gynecologists advises doctors to screen for marijuana use in pregnant women and encourage users to quit — even in cases when weed is being used for medicinal purposes — while carrying and breastfeeding.

“There are many concerns about prenatal marijuana use and the potential for adverse effects on the fetus,” said researcher Kelly Young-Wolff of the Kaiser Permanente Northern California Division of Research. “And although the health effects of prenatal cannabis use are complex and not well understood, no amount of cannabis has been shown to be safe during pregnancy.”

Despite that, Smith is part of a growing, but still small, group of women who are opting in. Aside from her husband, she just hasn’t told a soul about it because, according to her, “It’s too much of a risk socially and legally.”

Marijuana use among pregnant women in California doubled between 2009 and 2016

There’s no official screening system at the state or federal level for marijuana use in pregnancy in the US. And in many states, substance use during pregnancy is sufficient to make a child abuse or neglect report.

California a rare exception. And the best evidence on marijuana use while carrying a baby comes from Kaiser Permanente Northern California: It’s the only large health care system in the US that screens all pregnant women for prenatal marijuana use as part of standard prenatal care by urine toxicology and self-report. This means they have an objective way to measure whether it’s increasing or decreasing instead of relying solely on women’s self-reports.

In a study of that data, by Young-Wolff and her colleagues at Kaiser, they found a near doubling in the percentage of pregnant women who screen positive for marijuana use by self-report and/or a positive toxicology test between 2009 and 2016, from 4 percent to 7 percent.

Notably, the prevalence of marijuana use in their hospital system was nearly twice as high by toxicology testing versus what women reported to their doctors, suggesting that it’s probably more common during pregnancy than many people admit.

Trends in self-reported and biochemically tested marijuana use among pregnant Females in California From 2009 to 2016. JAMA

Weed was especially popular among younger moms: 22 percent of pregnant women under the age of 18, and 19 percent aged 18 to 24 years, screened positive for marijuana use in 2016, which shows that the younger generation may rely more heavily on marijuana during pregnancy. And Young-Wolff says the data from her hospital system reflects the national survey data we have on marijuana use during pregnancy, which also shows it’s going up.

It seems like this shift has something to do with with the swift changes in marijuana law and culture in recent years. In the November midterms alone, three more states decided to legalize recreational or medical weed. And dispensaries in places where weed is legal often market it directly at pregnant women. In a recent study on recommendations to pregnant women at Colorado cannabis dispensaries, researchers found the majority (69 percent) peddled products to treat morning sickness, and 36 percent told women the drug is safe to use in pregnancy.

Another study by Young-Wolff’s team at Kaiser Permanente found pregnant women with severe nausea and vomiting had four times greater odds of marijuana use than women without a nausea and vomiting diagnosis — though it wasn’t clear whether their morning sickness led them to use weed or weed exacerbated their morning sickness.

Either way, the marketing materials on cannabis products often omit an important point, Young-Wolff said: There’s a lot we don’t understand about marijuana’s health effects generally — and, in particular, on moms and babies, including the drug’s potential risks in pregnancy.

The hazy evidence on smoking weed in pregnancy

Since the late 1980s, researchers have known that THC — the active ingredient in cannabis — can cross the placenta and reach the fetus. More recently, researchers have found that THC is also secreted in breast milk up to six days after the last use. So that means the fetus is exposed to THC, and the concerns about marijuana’s health effects during pregnancy and lactation stem mainly from this fact.

One of the best summaries of the evidence on the health effects of cannabis comes from a major report out of the National Academies of Sciences, Engineering, and Medicine. More than a dozen experts reviewed more than 10,000 studies published between 1999 and 2016. (Most of the data in the review focused on smoked marijuana.)

Overall, the report suggested weed shows promise for chronic pain, multiple sclerosis, and cancer patients — but it also complicated the narrative that weed is a safe drug. The report found that it may increase the risk of respiratory problems (when smoked), schizophrenia and psychosis, getting into car accidents, and lagging social achievement. The report also uncovered pregnancy-related problems. In particular, the strongest link they uncovered showed that babies exposed to cannabis in utero tended to have lower birth weights.

“But what we couldn’t say is whether that’s a direct effect of marijuana or of smoking,” explained Marie Clare McCormick, a professor of maternal and child health at Harvard and chair of the National Academy of Sciences (NAS) committee that put out the report. The researchers noted that the marijuana birth weight findings were consistent with the effects of cigarette smoking on fetuses. McCormick explained that smoking any substance increases carbon monoxide in the blood, which reduces blood’s oxygen-carrying capacity, so not as much gets to the baby.

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“Clearly you can say, ‘Don’t smoke during pregnancy no matter what you’re smoking.’” But for the remainder, it’s the precautionary principle: Until we know more you probably shouldn’t do it,” McCormick summed up.

The NAS report drilled down into other health effects during pregnancy, like whether the babies of moms who used marijuana are more likely to wind up in the NICU or experience sudden infant death syndrome and cognitive and academic achievement challenges later in life. And on these important questions, it was equivocal: The researchers found “limited, insufficient, or no evidence.”

Still, the American College of Obstetricians and Gynecologists say that there are no approved indications or recommendations regarding prenatal marijuana use — even though the impact of prenatal cannabis use isn’t yet fully understood.

Even so, Young-Wolff said. “[There’s] sufficient evidence [of] an association between prenatal marijuana use and lower offspring birth weight, and limited research shows a correlation with some developmental delays or difficulties with executive functioning in the child — like problems with impulse control and attention.” And that’s enough to make health professionals wary.

Why marijuana bump science is so shaky

There are a few reasons why the research base on marijuana in pregnancy is so limited and inconclusive. Again, most of the evidence we have on weed’s health impact on the fetus comes from research on smoking — and there are many different ways people ingest cannabis nowadays, through edibles, oils, and vape devices to name just a few.

The THC content in weed has also shot up dramatically, which means it may be riskier to use while pregnant. So, as Young-Wolff of Kaiser told me, “A lot of the research that has been done is quite old” and doesn’t reflect the current marijuana landscape or the THC levels in today’s products.

The studies out there also tend to be small, without enough statistical power to accurately detect relationships; they often rely on self-reported data, which is flawed when it comes to substance use. A lot of the research also didn’t control for “confounding factors” or all the non-weed variables that may bias the results of studies.

“Pregnant marijuana users often use other drugs in pregnancy,” Young-Wolff explained, “and prior studies haven’t been able to differentiate which effects are due to marijuana or other drugs they may be using.”

Finally, the federal government still classifies marijuana as a Schedule 1 substance — the same legal and regulatory league as heroin — and that means researchers need to jump through all kinds of hoops to run studies.

The National Academies called for these restrictions to be relaxed so we can get a better understanding of the effects of marijuana in all kinds of different vulnerable groups. Erin Parker,* another weed-smoking mom, agreed. “I think it’s absurd to be passing laws making a drug legal and not having research on whether or not it’s safe for pregnant women.”

“They just need to reschedule [weed] so that it can be researched,” Smith reiterated. “If medical research came out and told me there were significant risks to my kids’ long-term health and development, I would listen to that research. But for now, like mothers have done since the beginning of time, I’m doing the best I can.”

*These names have been changed to protect the identity of the women.

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Cannabis dispensaries are marketing their products to pregnant women for morning sickness — but we don’t know if they’re safe. ]]>