Actually there are parts of the plant that can be poisonous from what Ive read. Here is an article about it.
"The indigenous elder tree of the western United States, Sambucus mexicana, can grow to 30 feet and produces small (1/4-inch), globular, nearly black berries that can be covered with a white bloom at maturity. The berries are juicy and edible when mature. The cooked berries are commonly eaten in pies and jams, and berry juice can be fermented into wine. The fresh leaves, flowers, bark, young buds, and roots contain a bitter alkaloid and also a glucoside that, under certain conditions, can produce hydrocyanic acid. The amount of acid produced is usually greatest in young leaves. There may be other toxic constituents in this plant. The root is probably the most poisonous and may be responsible for occasional pig deaths; cattle and sheep have died after eating leaves and young shoots. "