From Muppet Wiki

Insta-Grow Pills were invented by Dr. Bunsen Honeydew in The Muppet Movie. He and Beaker showed them to Kermit the Frog, Floyd Pepper, and Animal. He used it to make a prune become 8 feet, and explained that they work on anything, but the effect is sadly temporary. Animal soon took the pills and became a giant, scaring off Doc Hopper and his henchmen.

A jar of Insta-Grow Pills were later included as accessories with an exclusive Animal Action Figure.