Elderberry juice supports the immune system, but may be potentially harmful during pregnancy.Photo Credit Digital Vision./Photodisc/Getty Images. Elderberry, also known as elder, has been used for centuries in European countries for its ability to treat respiratory ailments as well as skin abrasions.his publication says there is no data suggesting elderberry preparations, including elderberry juice, might have adverse effects during pregnancy or lactation. Thus, elderberry may in fact be safe during pregnancy.