Lamar Odom's family and friends believe he's back on hard drugs -- and tell us they recently confronted the NBA star and questioned him about crack pipes in his home. 

Odom's history with crack is well-documented -- but people close to him thought he'd been scared straight after he overdosed at a Nevada brothel back in October. 

But multiple sources close to Odom -- hoping to get through to the NBA star -- tell us he's been acting very strange lately. His friends are convinced he's off the wagon, and for the last few weeks they've been trying to get through to him. 

So, a group of people went to his home to convince him to enter rehab -- but Odom scoffed ... telling the group he doesn't need any help. It sounds just like the failed intervention attempt from 2013. 

During the confrontation, which took place at Odom's home in Calabasas, we're told his friends noticed drug paraphernalia scattered all over the place ... including crack pipes, baggies and roaches. 

We're told the fear is that Odom believes he's invincible -- as evidenced by the fact he's been hitting bars and drinking while still recovering from the damage he suffered from the overdose. 

We reached out to Odom for comment -- so far, no word back.