Potion of Giant Size

From Storm King's Thunder, page 236.

Description
Potion, legendary.

When you drink this potion, you become Huge for 24 hours if you are Medium or smaller, otherwise the potion does nothing. For that duration, your Strength becomes 25, if it isn't already higher, and your hit point maximum is doubled (your current hit points are doubled when you drink the potion). In addition, the reach of your melee attacks increases by 5 feet.

Everything you are carrying and wearing also increases in size for the duration. When rolling damage for weapons enlarged in this manner, roll three times the normal number of dice; for example, an enlarged longsword would deal 3d8 slashing damage (instead of 1d8), or 3d10 slashing damage (instead of 1d10) when used with two hands.

When the effect ends, any hit points you have above your hit point maximum become temporary hit points. This potion is a pale white liquid made from the tongue of a giant clam, with a pungent aroma akin to that of rotting algae. It tastes sweet, however, when consumed.