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While we have adequate data to support the use of SSRI and SNRI antidepressants during pregnancy, there is less data regarding other classes of antidepressants. We typically do not use mirtazapine (Remeron) during pregnancy because the data regarding its reproductive safety has been sparse. A recent review documents the outcomes of infants exposed to mirtazapine (Remeron), reviewing 31 papers with a total of 390 cases of neonates exposed to mirtazapine during pregnancy or lactation. This is a very detailed review, providing detailed results of every study. Here is a summary of their findings:

Risk of Congenital Malformations: In a total of 334 mirtazapine-exposed cases, the incidence of major malformations did not differ from the incidence observed in children exposed to other antidepressants or non-teratogenic medications. Nine children (or 2.9%) of the mirtazapine-exposed children had major malformations.

Risk of Neonatal Symptoms: One study showed a trend toward increased risk of respiratory problems and hypoglycaemia; however, no other significant adverse effects on neonates were reported.

Breastfeeding: Four papers reported on 11 cases of exposure to mirtazapine through lactation. No adverse effects were detected.

Long-Term Neurodevelopment: Six papers reported on neurobehavioral development in a total of 22 cases. The studies varied considerably in terms of the assessments used and the age at which the assessments were performed (ranging from 1.5 months to 12 months). No adverse effects on behavioural development were reported.

The Bottom Line
While these data are reassuring and there is no indication that mirtazapine carries more risk than other antidepressants, the number of mirtazapine exposures remains small. Ideally we would like to have data from 600-700 exposures to get a better estimate of risk; basing decisions regarding safety on small sample sizes can lead to miscalculations of risk in either direction. Given the limited information on reproductive safety, we would continue to recommend using, if possible, other antidepressants with better characterized reproductive safety profiles.

That said, there may be situations where mirtazapine has certain benefits distinct from SSRIs and SNRIs. There have been several reports indicating that mirtazapine may be helpful for the treatment of hyperemesis gravidarum. Unlike typical serotonin reuptake inhibitor antidepressants, mirtazapine acts as an antagonist at the serotonin 5-HT3 receptor. This makes mirtazapine less likely to cause nausea; there is also suggestion that mirtazapine might have antiemetic effects, and mirtazapine has been used to treat nausea and vomiting in a variety of medical settings. Thus, this may be a situation where mirtazapine is preferred, even in the absence of adequate data on its reproductive safety.

Ruta Nonacs, MD PhD

Smit M, Dolman KM, Honig A. Mirtazapine in pregnancy and lactation – A systematic review. Eur Neuropsychopharmacol. 2016 Jan;26(1):126-35.

Next Week’s Essential Read: Screening for Perinatal Anxiety Disorders

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