The elderberry plant contains cyanogenic glycosides, a toxin that is removed by cooking. In one case, eight people experienced nausea and vomiting after drinking the juice made from freshly picked berries, including the leaves and branches. This is why people don’t usually recommend juicing raw elderberries or tossing them into a smoothie. Elderberries may also have diuretic properties, so use caution if you already take a medication that makes you pee more often.