Justin Bieber sizzurp addiction linked to crazy behavior?

Justin Bieber is hooked on sizzurp, Star reports. His ' time in London was marked by "increasing use of a deadly street drug," a source tells the magazine

"Everyone is worried about Justin," a "friend" tells Star. "He is smoking weed and drinking sizzurp nonstop, and it's starting to really affect him."

"It's gotten so bad that people are begging him to go to rehab," explains the mag's tipster.

The singer's friends are "begging him to enter rehab."