The possible side effects of consuming elderflower are largely dependent on the amount you’ve eaten and how you’ve prepared it. Generally speaking, the seeds, leaves, stems, and roots of the elderberry plant are considered toxic so if you’ve taken any of them together with the elderflower, you can expect side effects such as digestive system upset, nausea, diarrhea, and vomiting. An allergic skin reaction such as a rash is also possible.
That’s because of the cyanide-producing properties of the parts of the tree we mentioned. Cooking does remove this chemical but large enough quantities consumed too quickly can still lead to digestive distress.