Cory Monteith's friends are confident he will overcome his addictions.

The 'Glee' star recently checked into rehab after a surprising relapse but those close to him are confident he can put his problems - which have included alcohol and drugs in the past - behind him.

A source told People magazine: ''This latest slip came as a surprise. But people seem pretty certain he'll get better, he's been down this road before.

''On set his work ethic was strong and he always delivers, he was never known as one of the troublemakers.''

Cory's relapse was slow and reportedly started when he first made it in Hollywood.

A friend of the Canadian actor said: ''His choice to drink again happened gradually. He started out having one drink on occasion. Eventually I would see him and he was wasted. He acted differently when he was drunk.''

It was recently revealed Cory's girlfriend Lea Michele is responsible for urging him to get help for his ''substance addictions'' before they got out of hand.

A source said: ''She encouraged him to get help, she supports him completely.

''Though this was mostly Cory's decision, Lea agrees it's for the best. She's a great influence on him. All his friends can see Cory is incredibly happy with her.''