The tiny amount of belladonna in homeopathic remedies may pose little risk to adults, but children are a different story. Even low levels can cause muscle weakness, seizures, and difficult breathing. Belladonna contains several toxic ingredients, including a chemical called atropine. Atropine works by blocking a very common neurotransmitter in the parasympathetic nervous system—the part that controls unconscious bodily functions like breathing, urinating, digesting, and heartbeat. If applied directly to the eye, it also inhibits the muscle that controls your pupil, causing it to relax and your eye to dilate. This is why women used to use belladonna (meaning ‘beautiful woman’) to dilate their pupils, which apparently made them more attractive. It’s also why belladonna goes by another name: deadly nightshade. You can’t survive for very long when your parasympathetic nervous system is impaired, and it doesn’t take much belladonna to make your heart race and your breathing slow to dangerous levels.