If thrown, it will deal 1RBTDS/2GtI damage (2 if sticky). In Red Rescue Team, Blue Rescue Team, Explorers of Time, Explorers of Darkness, and Explorers of Sky, using this item in a dungeon will consume it, with no effect.
The Thunder Stone debuted in Electric Shock Showdown, when Nurse Joy gave Ash a Thunder Stone so that he could evolve his Pikachu in order to defeat Lt. Surge's Raichu. Pikachu, however, refused the offer. Ash kept the Thunder Stone in case Pikachu ever wanted to evolve; however, in Pika and Goliath!, a similar scenario occurred and Pikachu still refused to evolve. Seeing his determination to not evolve, Team Rocket stole the stone, planning to sell it.
An image of a Thunder Stone appeared in A Bite to Remember during Brock's explanation on how evolution works.
Ash had to find a Thunder Stone in a scavenger hunt as part of the Wishing Bell Festival contest in Climbing the Tower of Success!. He came across a young man in possession of one who tried to toss it to him from a long distance. The Thunder Stone nearly came in contact with Pikachu but he jumped out of the way just in time, leaving Ash to catch it.
In The Kindest Tentacruel, the Pokémon Fan Club Chairman told Yellow about a legend of an underwater dome at the bottom of Vermilion Harbor, housing a set of evolutionary stones which, unlike normal stones, did not disappear after making a Pokémon evolve, allowing them to be used repeatedly. The cause of Red's Poliwhirl's evolution had been one of these said stones, proving the legend to be true. Yellow was later led to the dome by a wild Tentacruel, finding a Leaf Stone in it, but the Fire, Thunder, and Water Stones were missing. Later, it was revealed that Giovanni had given them to Red so he could freely evolve and devolve his Eevee.
Through a glitch in the Generation I games, Pokémon that would normally require an evolutionary stone to evolve can be evolved without it, provided that the Pokémon levels up in the battle and the player has sent out a specific Pokémon in the same battle. In the case of the Thunderstone, this Pokémon is Growlithe.