Do WebRequest cause game to run slow?

Hello, I am working on an MMORPG and currently I am using WebRequest to pull information from my database. My server is a DarkRift Networking 2 server that has been converted into a Unity console. I use WebRequest to get information about the user from a php file. I was wondering, does WebRequest perhaps use some sort of threading method? I've heard that using it may slow down the progress of my game. I am going to be beta testing my game soon, so I'll find out eventually, but, I just wanted to know before hand in case I may want to find another solution for getting information out of my MySql database. Currently, Unity doesn't have a lot of support for MySql and I was trying to see if there's a better solution. I don't want to keep using the WebRequest to pull each piece of information I need about the user every time. I was hoping using another method would perhaps increase the performance and won't create lag for other players.