Weird. I have eaten ( sucked the juice) Elderberries and had no side effects or problems.
also a common, oldfashioned way to make cordial from them in Sweden is to steep the raw berries with sugar and mash them up, then collect the juice.
Elderberries are used for cordial and wine. The flowers also. I suppose the fermentation or heating for cordial must temper them a bit. The flowers are good too. It's a non-toxic plant, just don't overdo it.
Some of my 'smallest room' moments are caused by wild bilberries. I love them. In my youth, scrumping plums led to a very grumpy tum. Was fun though, gorging on fruit.
I seem to recall Marlowe from Wild Food UK saying that other species of elder are poisonous, perhaps he was referring to dwarf elder. White bryony is another poisonous berry found here. There are a couple vaguely resembling redcurrants that are I think, also worth emphasising that spindle and cuckoo pint are poisonous (the latter very poisonous and unpleasant) as these two are by far the most common of the toxic ones in my experience.