Can my medicine effect my pregnancy test results?

Smiling woman with pregnancy test strip and giving thumbs up
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In my line of work, one question that many women ask me: What medications can cause a false negative pregnancy test?

In general there are not many medications that will affect the results of your pregnancy test. This is true of both positive and negative results. The reason is that the pregnancy test is based on the levels of human chorionic gonadotropin (hCG) in your urine or blood. The vast majority of medications do not have any way to suppress the hCG nor increase it.

 

What about antibiotics?

Antibiotics are given to help your body fight an infection or to prevent an infection. These medications do not contain hCG. They can, however, alter how your birth control, specifically oral contraceptives (the pill), work. This means that you may be more likely to get pregnant if you are on the pill and take antibiotics. Be sure to let your prescribing doctor or nurse know that you take the pill if you are given antibiotics. They can guide you on how to use a backup method of birth control and for how long.

What about birth control pills?

Birth control pills and other forms of birth control do not affect the results of a pregnancy test urine or blood. This is because they do contain hCG, nor do they alter your hCG levels, or cause to secret hCG, except in the case of a pregnancy (meaning your birth control failed you).

What about illegal or recreational drugs? 

Alcohol, marijuana, cocaine, cigarettes, none of these will cause you to have a false positive or negative pregnancy test.

Some may make you more likely to get pregnant because of riskier behavior when under the influence of some, like not using birth control and having sex, but they will not alter the findings on your pregnancy test.

Medications Causing False Positive Pregnancy Test Results

The only medications really known to cause false results, false positives specifically, are those medications containing hCG.

These drugs are used in conjunction with infertility treatments. In these cases your doctor or fertility center will tell you not to take a pregnancy test until these medications have cleared your system. They will give you specific instructions for when and where to take a pregnancy test. And in the case of a blood pregnancy test, you may have to have the results repeated.

What to Do If You Think Your Pregnancy Test is Wrong

If you have taken a pregnancy test and think it is giving you the wrong answer, the first thing would be to wait a few days and test again. Many times, you simply tested too early and got a false negative because your body's hCG was not detectable yet. If you have a positive test and you think it is wrong, or you are still having a negative test and you think it is wrong, it is time to make an appointment with your doctor or midwife for a physical exam. This will help end all of the doubt.

Source:

Anderson, L. Pregnancy Test Guide. March 11, 2013.

Cole LA. The utility of six over-the-counter (home) pregnancy tests. Clin Chem Lab Med. 2011;49:1317-22.

Mayo Clinic Staff. Home pregnancy tests: Can you trust the results? http://www.mayoclinic.org/healthy-lifestyle/getting-pregnant/in-depth/home-pregnancy-tests/art-20047940 Accessed February 9, 2016.

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