The Infertility Potion has the ability to, when consumed, make one barren from being able to have children; though these effects have been proven reversible when drinking the waters of Lake Nostos.
Before the Curse
Regina drinks an infertility potion to hurt her mother. ("Mother")
At an unknown point, King George's wife drinks an infertility potion, thus making her unable to conceive a child; because of this, the couple go to Rumplestiltskin, who procures them James. ("Lady of the Lake") Realizing Cora set her up with the Sheriff of Nottingham simply to get her daughter pregnant, Regina stays a step ahead and gets together an infertility potion in order to make herself barren. Though Cora claims Regina needs to start a dynasty and win the kingdom's love, the Evil Queen suspects her mother to have other motives, those being to eventually kill her and take power through her heir. She proceeds to drink the potion, which causes intense pain; before leaving, Cora states that Regina is responsible for her own unhappiness. ("Mother") Now amidst a war against King George, Snow White finds herself taken prisoner by the King, and when accepting a drink, she realizes it's been rigged with an infertility potion, used to punish Charming. Snow keeps this from her beloved, focusing on getting his wounded mother, Ruth, to Lake Nostos in order to heal her with its water. Ruth comes to learn of Snow's new condition though, and she ends up sacrificing the last few droplets they could find of the water to heal her future daughter-in-law, and she and Charming can go on to have children of their own. She later passes, having witnessed their private wedding ceremony. ("Lady of the Lake")