First, MD5 is a cryptographics HASH, NOT an encryption.
Second, it's a ONE-WAY hash. There is no such thing as "decrypting a hash". In theory, you cannot get the original content back from a hash value.
Lastly, MD5 is considered broken and should no longer be used in production code. It just doesn't take that much computing power to break it in todays world. Also, two different pieces of content CAN produce the same hash value using MD5!
Use something a bit stronger, like SHA512 instead and use proper salting techniques to make it even harder to break.