Venlafaxine (Effexor®) Use in Early Pregnancy and Birth Defects: A Patient's Guide to the Research

Table of Contents

• Key Points
• Why This Study Matters
• How the Research Was Conducted
• Key Findings: What the Researchers Discovered
• Findings for Isolated Birth Defects
• Additional Analyses: Testing the Strength of the Results
• Clinical Implications: What This Means for Patients
• Study Limitations: What This Study Couldn't Prove
• Recommendations for Patients
• Frequently Asked Questions
• Source Information

Key Points

• In a large U.S. analysis, mothers of babies with birth defects were more than twice as likely to report venlafaxine use around conception than mothers of healthy babies.
• Statistically significant associations were found for anencephaly, atrial septal defect, coarctation of the aorta, cleft palate, and gastroschisis, but exposed numbers were small.
• The findings show associations, not proven cause and effect; researchers say additional studies are needed before firm conclusions can be drawn.
• Do not stop venlafaxine suddenly; untreated depression itself carries risks for mother and baby. Talk to your doctor about risks, benefits, and alternatives.
• Venlafaxine users in this analysis were more likely to take folic acid, which is known to reduce neural tube defect risk; all women who could become pregnant should take it.

Why This Study Matters

Depression and anxiety are common conditions that affect many women of childbearing age. In fact, about 18% of pregnant women experience depression, and an estimated 8.5% experience generalized anxiety disorders. For many of these women, antidepressant medications are an essential part of treatment.

Venlafaxine, sold under the brand name Effexor®, is a type of antidepressant known as a serotonin-norepinephrine reuptake inhibitor (SNRI). It works by blocking the reuptake of two key brain chemicals—serotonin and norepinephrine—and at high doses, it may also affect a third chemical called dopamine. This mechanism is similar to another widely used class of antidepressants called selective serotonin reuptake inhibitors (SSRIs), which block only serotonin. SSRIs include medications like fluoxetine (Prozac®), sertraline (Zoloft®), and paroxetine (Paxil®).

While many studies have examined the safety of SSRIs during pregnancy, much less is known about SNRIs like venlafaxine. Previous research has produced mixed results for SSRIs, with some studies suggesting possible links to heart defects, particularly septal defects (holes in the heart's walls) and a type of heart condition called right ventricular outflow tract obstruction (RVOTO). However, venlafaxine has rarely been studied on its own—many earlier studies grouped it together with SSRIs or other newer antidepressants, making it impossible to determine whether venlafaxine carries its own specific risks. This study was designed to fill that critical gap.

This matters for patients because many women who take venlafaxine become pregnant or are already pregnant when they start treatment. Understanding whether this medication is linked to birth defects is essential for making informed decisions about mental health care during pregnancy.

How the Research Was Conducted

The researchers used data from the National Birth Defects Prevention Study (NBDPS), one of the largest studies of birth defects ever conducted in the United States. The NBDPS is a population-based, case-control study, meaning it compares mothers of babies with birth defects (cases) to mothers of babies without birth defects (controls) from the same geographic areas and time periods.

Study Participants and Locations

Data were collected from ten birth defects surveillance systems across the United States:

• Arkansas (statewide)
• California (region near Fresno)
• Georgia (metropolitan Atlanta)
• Iowa (statewide)
• Massachusetts (eastern counties)
• New Jersey (statewide, through 2002)
• New York (western NY and Hudson Valley)
• North Carolina (19 central counties, beginning in 2003)
• Texas (varying regions)
• Utah (statewide, beginning in 2003)

The analysis included mothers with estimated dates of delivery (EDD) between October 1, 1997, and December 31, 2007. A total of 27,045 mothers met the inclusion criteria: 19,043 case mothers whose babies had one of 30 selected birth defects, and 8,002 control mothers whose babies had no birth defects.

Defining Cases and Controls

Cases included live births, stillbirths (at least 20 weeks of gestation), and elective terminations where the baby was diagnosed with one of more than 30 major structural birth defects. Babies with recognized or strongly suspected chromosomal abnormalities or single-gene disorders were excluded to focus on birth defects of unknown cause. All case records were reviewed by clinical geneticists, and heart defect diagnoses were confirmed using reports from echocardiography, cardiac catheterization, surgery, or autopsy by pediatric cardiology experts.

Control infants were randomly selected from hospital birth records or birth certificate records from the same populations and time periods as the case infants. These babies had no birth defects.

Interviews and Data Collection

Mothers were contacted within 6 weeks to 24 months after delivery. Trained interviewers administered a standardized computer-assisted telephone interview in English or Spanish, covering a wide range of topics including:

• Maternal and paternal demographic characteristics
• Pregnancy history
• Medication and vitamin use (including folic acid)
• Dietary details
• Drug and alcohol use
• Occupational exposures
• Reproductive health information

Defining Venlafaxine Exposure

Exposure was defined as any reported use of venlafaxine from one month before conception through the third month of pregnancy (a period called the periconceptional window). The researchers chose this broader timeframe because women may not recall exact dates of pregnancy or medication use with perfect accuracy.

One important detail about the data collection: for births with EDDs during 1997–2005, venlafaxine was not one of the specific medications listed in the interview. Mothers could still report it as an "other" medication they had taken. However, in 2005, the interview was revised, and Effexor® (the more commonly recognized brand name) was added to the list of medications read aloud to mothers. This means that for births from 2006–2007, mothers were specifically asked whether they had taken venlafaxine, which may have increased reporting accuracy in those years.

Statistical Methods

The researchers calculated adjusted odds ratios (aORs) and 95% Fisher's Exact confidence intervals (CIs) for 24 birth defect groups that had at least 400 case mothers interviewed. They adjusted for two factors chosen in advance:

• Maternal age (under 30 vs. 30 and older)
• Race/ethnicity (non-Hispanic white vs. other)

Because gastroschisis is associated with young maternal age, that analysis used a different age cutoff (under 20 vs. 20 and older).

Several important groups of mothers were excluded from the analysis. Mothers with pre-pregnancy type 1 or type 2 diabetes were excluded because diabetes is strongly associated with birth defects and could confound the results. Mothers who reported using other antidepressants during the periconceptional period were also excluded, allowing the researchers to isolate effects specific to venlafaxine. Finally, mothers with missing information about medication timing, or who used venlafaxine only outside the periconceptional window, were excluded. Women were classified as unexposed if they did not report any antidepressant use from three months before conception through the end of pregnancy.

Key Findings: What the Researchers Discovered

The study found that 0.17% (14 of 8,002) of control mothers and 0.40% (77 of 19,043) of case mothers reported using venlafaxine during the periconceptional period. In other words, mothers of babies with birth defects were more than twice as likely to have used venlafaxine early in pregnancy.

Who Was Most Likely to Use Venlafaxine?

Venlafaxine use was not evenly distributed across all mothers. The researchers found that exposure was more common among:

• Mothers with higher education levels
• Non-Hispanic white mothers
• Mothers who used folic acid from one month before conception through the first month of pregnancy

This is important context, because these factors themselves could influence pregnancy outcomes and need to be accounted for when interpreting the results.

Duration of Use

Mothers who used venlafaxine reported taking it for periods ranging from 1 to 120 days. Notably, the majority—54%—reported using the medication for the entire period from one month before pregnancy through the end of the first trimester, suggesting long-term, ongoing treatment rather than short-term occasional use.

Exposure also increased over time. Only 24% of exposed mothers had babies with EDDs during 1997–2002, while 76% had EDDs from 2003–2007. This trend mirrors broader increases in antidepressant use among pregnant women in the United States during that period.

Birth Defects Linked to Venlafaxine

Of the 24 birth defect groups analyzed, seven were not assessed because there were too few exposed mothers. One group, esophageal atresia (a condition where the esophagus doesn't connect to the stomach, n=499), had no mothers exposed to venlafaxine at all. Six other groups had two or fewer exposed mothers: anotia/microtia (ear malformations), d-transposition of the great arteries (a severe heart defect), tetralogy of Fallot (a complex heart defect), hypoplastic left heart syndrome (an underdeveloped left heart), anorectal atresia (a malformed anal opening), and diaphragmatic hernia (a hole in the diaphragm).

For the remaining 17 groups, all effect estimates were elevated (meaning venlafaxine use was more common among case mothers than control mothers), but only five associations were statistically significant:

1. Anencephaly — a severe neural tube defect where the brain and skull fail to develop fully
2. Atrial septal defect (ASD) secundum or ASD not otherwise specified — a type of hole in the wall between the heart's upper chambers
3. Coarctation of the aorta — a narrowing of the aorta, the body's main artery
4. Cleft palate — an opening in the roof of the mouth
5. Gastroschisis — a condition where the baby's intestines protrude through a hole in the abdominal wall

The association with septal heart defects appeared to be driven by the ASD subcategory, and the association with left ventricular outflow tract obstruction (LVOTO) defects appeared to be driven by coarctation of the aorta. In plain terms, this means that when the researchers looked at broader categories of heart defects, the significant links were specifically tied to these particular subtypes.

Findings for Isolated Birth Defects

Because some babies have more than one birth defect, the researchers conducted a sub-analysis restricted to babies with isolated birth defects (meaning just one defect, with no other major malformations present). This helps determine whether venlafaxine is specifically associated with a particular defect rather than with multiple anomalies in general.

The majority of associations remained statistically significant in this analysis, but there were some notable changes:

• Anencephaly: The association increased slightly, with a crude odds ratio (cOR) of 6.2 (95% CI: 1.5–20.0)
• Cleft palate alone: The association increased, with a cOR of 4.4 (95% CI: 1.5–11.6)
• Gastroschisis: The association increased, with a cOR of 4.2 (95% CI: 1.3–11.7)
• LVOTO defects: The association decreased, with a cOR of 3.1 (95% CI: 1.1–8.3)
• Coarctation of the aorta: No longer statistically significant, with a cOR of 3.5 (95% CI: 0.8–11.1)

These numbers require careful interpretation. A cOR of 6.2 does not mean a 6.2% risk—it means that in this study, babies with anencephaly were about 6 times more likely to have been exposed to venlafaxine than babies without birth defects. Because birth defects are rare, even a 6-fold increase translates to a small absolute risk for any individual woman.

Additional Analyses: Testing the Strength of the Results

After seeing the initial results, the researchers ran several "post-hoc" analyses (analyses conducted after the main results were known) to better understand what they were finding and whether the associations could be explained by factors other than venlafaxine itself.

Analysis of the Most Recent 5-Year Period

Since fewer mothers with EDDs from 1997–2002 reported using venlafaxine, the researchers limited the data to the most recent five-year period (EDD: 2003–2007). The associations remained elevated, but most were no longer statistically significant, likely due to smaller sample sizes. The associations with anencephaly and LVOTO defects remained statistically significant, while cleft palate and gastroschisis were of borderline significance.

Other Medications and Illnesses

Could the birth defects be caused by other medications that venlafaxine users also took, or by underlying illnesses? The researchers examined this carefully:

• 2.6% of exposed case mothers (2 of 77) also used high blood pressure medications
• 9.0% of exposed case mothers (7 of 77) also used antiepileptic medications (none used valproic acid, which is known to cause birth defects)
• 2.6% of exposed case mothers (2 of 77) also used opioid analgesic medications

No consistent patterns emerged. For example, three case mothers exposed to venlafaxine also took clonazepam (an antiepileptic medication), yet each of their babies had a completely different condition: one had cleft palate, one had a combination of heart defects (ASD and ventricular septal defect), and one had tetralogy of Fallot. Similarly, when mothers were asked open-ended questions about any illnesses during pregnancy, no pattern of disease was found among venlafaxine-exposed mothers.

Testing for Recall Bias

One concern in case-control studies is recall bias: mothers who have had a baby with a birth defect may remember and report medication use more thoroughly than mothers of healthy babies. To explore this, the researchers conducted a hypothetical analysis. They assumed that 30% of exposed control mothers had failed to report their venlafaxine use—meaning that in addition to the 14 control mothers who did report exposure, 6 more (out of a hypothetical total of 20) were actually exposed but didn't mention it.

Even under this scenario of significant under-reporting, all associations remained elevated, though they moved closer to the null (no effect):

• Anencephaly decreased to 3.9 (95% CI: 1.1–11.8)
• Coarctation of the aorta decreased to 3.1 (95% CI: 1.0–8.1)
• Cleft palate alone decreased to 2.5 (95% CI: 0.9–6.1)

This analysis suggests that even if some mothers of healthy babies forgot to report venlafaxine use, the observed associations would likely persist, although they would be weaker.

Clinical Implications: What This Means for Patients

These findings are important but require careful context. First, it's worth emphasizing that this study found associations, not proof of cause and effect. The researchers themselves note that their findings differ from some earlier studies. For instance, a prospective cohort study by Einarson and colleagues compared women exposed to venlafaxine with women exposed to SSRIs and with women using medications believed to be safe during pregnancy (about 150 women per group). They found no significant differences in birth defect rates, but the study was small and lacked the statistical power to detect associations with rare birth defects.

Another study by Oberlander and colleagues, which used linked administrative health data and prescription records, found no increased risk of birth defects overall or of cardiovascular defects among women exposed to venlafaxine in the first trimester compared to women not exposed to SSRIs, SNRIs, or benzodiazepines.

What About the Biology?

The researchers also explored whether there is a plausible biological explanation for the associations they observed. Venlafaxine works by blocking the reuptake of the neurotransmitters serotonin and norepinephrine. During embryonic development, these same chemicals are present very early and may act as morphogens—signaling molecules that influence how cells develop in a dose-dependent way. This means that if a medication changes the levels of these chemicals at a critical moment of development, it could potentially interfere with normal formation of the face, heart, and other structures.

Animal studies have provided specific evidence that serotonin plays a role in craniofacial (face and skull) and cardiac development, and that norepinephrine influences the formation and differentiation of neural crest cells—cells that go on to form many parts of the face, heart, and nervous system. One animal study reported adverse effects on rat fetuses exposed to venlafaxine, while studies on rats and rabbits performed by the manufacturer found no teratogenic effects. The researchers note that their findings of associations with septal heart defects, LVOTO defects, and cleft palate are consistent with the biological hypothesis that venlafaxine could disrupt these early developmental pathways.

The Role of Depression Itself

There is another important consideration: the "confounding by indication" problem. Venlafaxine is often a second-line treatment, prescribed to people who have not responded well to first-line treatments like SSRIs. This means women taking venlafaxine may have more severe depression or different underlying characteristics than women taking other antidepressants. Depression itself has been linked to adverse pregnancy outcomes, including spontaneous abortion, fetal death, low birth weight, and preterm birth. In this study, over 50% of venlafaxine-exposed mothers used the medication for the entire early pregnancy period, indicating long-term treatment. The researchers acknowledge that because they did not have specific questions about depression in their interview, they were unable to separate the effects of the medication from the effects of the underlying disease.

For patients, this is a crucial point: the question is not simply whether venlafaxine causes birth defects, but whether the risk of taking the medication is greater or less than the risk of untreated or inadequately treated depression during pregnancy.

Study Limitations: What This Study Couldn't Prove

Every scientific study has limitations, and the researchers were transparent about several important ones:

• Small numbers: Only 77 case mothers and 14 control mothers reported venlafaxine exposure. This resulted in wide confidence intervals, meaning the true risk could be considerably lower or higher than the estimates suggest.
• Recall bias: Because interviews took place after the birth outcome was known, mothers of babies with birth defects may have remembered medication use more completely than mothers of healthy babies. Although the hypothetical analysis suggested the associations would persist, recall bias cannot be fully eliminated.
• Changes in data collection: Venlafaxine was not specifically listed in the interview for births during 1997–2005, potentially leading to under-reporting in earlier years.
• Inability to assess confounding by indication: The study lacked detailed information about depression severity, so it could not determine whether the associations were due to venlafaxine itself or to the underlying depression it was treating.
• Pre-existing differences: Venlafaxine users differed from non-users in several ways (education, race/ethnicity, folic acid use), and while the analysis adjusted for age and race/ethnicity, other unmeasured differences could exist.
• No information on dosage: The analysis did not examine whether higher doses of venlafaxine carried greater risks, which would be an important area for future research.
• Seven birth defect groups couldn't be assessed due to too few exposed cases, meaning the study cannot rule out associations with those specific defects.

Perhaps most importantly, the researchers note that previous studies using different designs (prospective cohorts and administrative databases) did not find significant associations with venlafaxine. The differing results could reflect true differences, variations in study methodology, or the play of chance.

Recommendations for Patients

If you are pregnant, planning to become pregnant, or taking venlafaxine (Effexor®), here's what you should keep in mind based on this research:

1. Do not stop taking your antidepressant without talking to your doctor. Suddenly stopping an antidepressant can cause withdrawal symptoms, worsening depression, and other complications. Untreated depression itself carries risks for both mother and baby.
2. Have a conversation with your healthcare provider before pregnancy or as early in pregnancy as possible. Discuss the potential risks and benefits of venlafaxine compared to other treatment options. Your doctor can help you weigh the evidence, including this study's findings, in the context of your individual mental health history.
3. Ask about alternative treatments. Because venlafaxine is often used as a second-line treatment, you may have other options to consider. SSRIs have been studied more extensively during pregnancy, though they also carry some possible risks. Non-medication approaches, such as psychotherapy, may also play a role in your treatment plan.
4. Consider your overall risk profile. This study found associations with specific birth defects, but the absolute risk for any individual baby remains small. For example, even a 6-fold increase in anencephaly risk must be viewed against the baseline risk, which is roughly 1 in 5,000 births. Discuss what these numbers mean for your specific situation.
5. Take folic acid. The study found that venlafaxine users were actually more likely to take folic acid, which is good—folic acid is known to reduce the risk of neural tube defects including anencephaly. All women who could become pregnant should take a daily folic acid supplement (typically 400–800 micrograms).
6. Be honest with your doctor about all medications you take. This research underscores how important it is for healthcare providers to know exactly which medications a pregnant woman is using, so they can monitor appropriately and make informed recommendations.
7. Remember that this is one study, not the final word. The researchers explicitly state that "additional studies are needed to confirm these results." The scientific process works slowly, and recommendations may evolve as more research becomes available.

Ultimately, the decision about how to manage depression or anxiety during pregnancy is deeply personal and should be made collaboratively with your healthcare provider, taking into account your medical history, the severity of your symptoms, your treatment goals, and the best available evidence.

Frequently Asked Questions

I take venlafaxine (Effexor) and just found out I'm pregnant. What should I do?

Do not stop your antidepressant without talking to your doctor, because suddenly stopping can cause withdrawal, worsening depression, and complications. Have a conversation with your healthcare provider as early as possible to weigh the potential risks and benefits of venlafaxine versus other options, including non-medication treatments, based on your specific mental health history.

Which birth defects were linked to venlafaxine use around conception?

In this large U.S. analysis, statistically significant links were found for five specific birth defects: anencephaly, a type of heart hole called atrial septal defect, coarctation of the aorta (narrowing of the main artery), cleft palate, and gastroschisis (intestines protruding through the abdominal wall). However, the number of exposed mothers was small.

What does a 6 times higher risk mean for my baby?

It means that in this analysis, babies with anencephaly were about 6 times more likely to have been exposed to venlafaxine than babies without birth defects. Because birth defects are rare, even a 6-fold increase translates to a small absolute risk. For example, baseline anencephaly risk is roughly 1 in 5,000 births.

Why should I not stop taking venlafaxine suddenly if I'm concerned about birth defects?

Suddenly stopping an antidepressant can cause withdrawal symptoms, worsening depression, and other complications. Untreated depression itself carries risks for both mother and baby. The researchers could not separate the medication's effects from the effects of the underlying depression, so stopping abruptly may pose its own dangers. Always discuss any changes with your doctor.

Did this research prove that venlafaxine causes birth defects?

No, it found associations, not proof of cause and effect. The researchers emphasize that exposed mothers were few and additional studies are needed before firm conclusions can be drawn. Previous studies using different designs did not find significant links, so this is not the final word.

What were the main limitations of this study?

Only 77 case mothers and 14 control mothers reported venlafaxine exposure, producing wide confidence intervals. Mothers were interviewed after birth, so recall bias was possible. Venlafaxine wasn't specifically listed in interviews before 2005, potentially causing under-reporting. Researchers also lacked detailed information about depression severity and did not examine dosage.

What should I ask my doctor about venlafaxine in pregnancy?

Ask about alternative treatments, since venlafaxine is often a second-line option and SSRIs have been studied more extensively. Discuss your overall risk profile, including what these findings mean for your specific situation. Also ask about folic acid supplementation, and be honest about all medications you take so your provider can monitor appropriately.

Source Information

Original Article Title: Venlafaxine Use in Early Pregnancy and Birth Defects

DOI: 10.1002/bdra.23096

Authors: Kara ND Polen, MPH; Sonja A Rasmussen, MD, MS; Tiffany Riehle-Colarusso, MD, MPH; Jennita Reefhuis, PhD; and the National Birth Defects Prevention Study

Affiliation: National Center on Birth Defects and Developmental Disabilities, Centers for Disease Control and Prevention, Atlanta, GA

Journal: Birth Defects Research Part A: Clinical and Molecular Teratology, Volume 97, Issue 1 (January 2013), pages 28–35. doi:10.1002/bdra.23096

Publication Date: Published online in final edited form in January 2013; available in PMC June 29, 2015.

Funding/Disclaimer: The findings and conclusions in this report are those of the authors and do not necessarily represent the official position of the Centers for Disease Control and Prevention. The study was presented at multiple scientific meetings between 2010 and 2011, including the Society for Pediatric and Perinatal Epidemiologic Research, the Society for Epidemiologic Research, the Teratology Society, the David W. Smith Workshop on Malformations and Morphogenesis, and the International Conference on Pharmacoepidemiology and Therapeutic Risk Management.

This patient-friendly article is based on peer-reviewed research. It is intended for educational purposes and should not replace professional medical advice. Always consult your healthcare provider about medication decisions during pregnancy.