Onions are not a nightshade.
Onions, including red onions, are not in the Solanaceae or nightshade family.
While the potato and tomato are common foods around the world, some in this family, like the black nightshade plant (Solanum nigrum), are extremely toxic.
Plants in the Solanaceae family are informally referred to as nightshade plants.
The onion family is completely separate from nightshades.
Nightshades include potatoes, tomatoes, pepper, eggplant, tobacco.
Nightshade is a family of plants that includes tomatoes, eggplant, potatoes, and peppers.
Tobacco is also in the nightshade family.
Nightshades are unique because they contain small amounts of alkaloids.
Some vegetables that are also not nightshades include.
Black pepper.
Coffee.
Cucumbers.
Garlic.
Spinach.
Sweet potatoes.
Zucchini.