It’s diphenhydramine, or Sudafed. Also sometimes sold as Unisom but to be distinguished from the Unisom that is Doxylamine. My 18-mo old had the paradoxical reaction.
- diphenhydramine aka Benedryl is an antihistamine with a common side effect of sleepiness
- doxylamine aka Unisom is also an antihistamine but these days people only really use it as a sleep aid or for nausea
- psuedoephedrine aka Sudafed is a decongestant. Not sold over-the-counter because it can be used to make meth. It's a stimulant and appetite supressant
Finally, there's "Sudafed PE" aka phenylephrine, which is also sold as a decongestant but it (literally) doesn't work
