The "Umbrella" singer says the troubled star - who recently lost custody of her two children to ex-husband Kevin Federline following her erratic behavior - is under too much pressure and thinks people should leave her alone.
She said: "I don't think there's anything wrong with partying, partying is healthy. You can't have a boring life. You have to party some time."
"People put so much energy into being negative about Britney. There's so much pressure on her - it can't be easy."
Although she is worried about the pressures of fame, Rihanna isn't concerned about having a high-profile relationship.
The sexy star is currently dating actor Josh Hartnett and admits she is smitten with him.
She said: "I would be lying if I said we were just good friends. I have so fallen for him - he is lovely."
"He's so hot and he's really sweet to me. When we hang out, it feels right, even though it's pretty new."
