Rihanna has admitted that she can't trust people now she's famous.

The 20-year-old singer said she always keeps her guard up around men and can be quite judgemental.

Speaking to more! magazine, she said: "I always have my guard up with men, no matter who they are. There are people who love you just because you're famous.

"But I'm good at reading people and I'm not naive."

She added: "The longer I'm in this business, the more judgemental I am. I can't deal with dishonesty. People often try to be your friend or get with you and then when you're not in the spotlight, they don't want to know you."

The Umbrella star is has reportedly been dating R&B star Chris Brown for nine months, but neither of them have publicly admitted they are in a relationship, despite being regularly photographed together.

Rihanna also said her busy lifestyle means that she finds it hard to meet friends.

She said: "I have my best friend, Melissa, from home with me right now. It's great I can fly my friends around the world.

"Staying down to earth isn't easy, but I'm strong and when I feel lost, I just call Melissa. When I see people turning to drugs and alcohol, then that's when I call her. She helps me."

She also revealed that her latest single, Rehab, was written with singer Justin Timberlake, which she said was very exciting.

"For him to write a record for me was such a big deal. I was so excited, as I'm a huge fan of his. But it came together very quickly."

Rihanna's new album Good Girl Gone Bad: The Remixes is out on February 9.