Birch sap

The Birch sap is a concoction the Treeminders of Oasis give to outsiders as part of a purification ritual before they are allowed to meet The Great One (also known as Harold). The Vault 101 Dweller will pass out after drinking the sap and wake up a while later. According to Harold the Birch sap have varying effects, amongst which hysteria seem to be common. This is what seem to have happened to the Wasteland Merchant that you can meet as a random encounter.