From Pokémon Online Wiki
|Introduced in Gen 1|
|Has a 10% chance to lower the target's Speed by one stage.|
Constrict has a 10% chance to lower the target's Speed by one stage.
 Generation 1-5
 Competitive Usage
Consrict is the weakest move in Pokémon (that actually does damage), and every Pokémon that gets it has a better move to use.