Simpson and Son Revitalizing Tonic is an aphrodisiac sold by Grampa and Homer.
The tonic was purportedly first developed by Grampa's great-grandfather Howland Simpson when he was trying to develop a cheap substitute for holy water. Grampa makes the tonic by mixing a variety of bottles kept in his bathroom cabinet, which appear to include several types of medicine/ointments/colognes. After being stirred together, the tonic has a brownish-red color. When consumed, the tonic takes effect rapidly, after only a few seconds. While the effects on women have yet to be shown, in men it quickly triggers a state of sexual arousal that leads to increased sexual performance which can even lead to euphoric memory loss (as in the case of Homer's first use of the tonic).
Homer and Grampa first put the tonic for sale at $1 per bottle; when Homer had trouble advertising the tonic, Grampa's soapboxing led to massive sales. The two went on a weekend-long "Traveling Medicine Show" to advertise the tonic, but the partnership quickly faultered when Homer failed as a shill. After visiting the house Homer grew up in ( which was foreclosed in 1963), a further fight during the car ride home led to Grampa revealing that the tonic was responsible for Homer's birth, and that Homer was a mistake. This caused Homer to kick Grampa out of the car, and the two discontinued their partnership. Grampa attempted to continue selling the tonic with Barney Gumble, but the new partner proved to be a failure for advertising the product.