Would Effexor or Bactrim cause a false positive pregnancy test?

Posted on Sat, 23 Jun 2012 in Pregnancy
Question: My girlfriend is about 9 days late, she's taking 112.5mg of Effexor (venlafaxine) and recently diagnosed with a staff infection so she's taking Bactrim DS and sulfamethoxazole with trimethoprim. She took two home pregnancy tests last night and they were both positive. Would any of those drugs cause a false positive? She probably should have saved a test for a morning test.
Answered by Dr. Hema Yadav 51 minutes later
Thanks for posting your query.
Urine pregnancy tests detect the presence of HCG hormone in your urine which is elevated and excreted by body in pregnancy.
Though many drugs are speculated to cause false positive test the only conclusive evidence for false positive tests apart from misinterpretation or technical errors are any drug or injection containing the hormone HCG or any cancers or medical illness or undue stress raising the body level for HCG.
According to your details , it doesn't seem that the medications taken by you are causing false positive test.The morning sample does give a better result since it has more chances of concentration of hcg in urine .
But in your case since the night sample itself has been positive , I would suggest you go for a blood hcg level testing which is quantitative and wil confirm if pregnancy or some other condition is causing the positive test.
Alternatively you can consult your gynaecologist and she can interpret the blood tests result and also advise for ultrasound if required for confirmation.
Please do not take undue stress as it will just add to your problem, instead act promptly and be safe than sorry.
Above answer was peer-reviewed by : Dr. Raju A.T
Answered by
Dr. Hema Yadav

Pediatrician, Infectious Diseases

Practicing since :2005

Answered : 1528 Questions


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