Richard Taite, an addiction-recovery expert, says Nick Reiner‘s relationship to his famous father and grandfather may have led to problems of self-worth as he grew up … and he says Nick’s struggles and extensive history in rehab may have been a result.

As you know, Nick Reiner is charged with murdering his parents, Rob and Michele Reiner … and Nick had earlier been in and out of rehab for substance abuse, and was diagnosed with schizophrenia before the tragedy.

Taite — the founder and executive chairman of Carrara Treatment — points out mental illness is almost always attached to drug addiction and alcoholism saying … “they’re one and the same.”

Richard says it’s common for celebrity children to feel this pressure and check into rehab treatment for substance abuse when they feel their success doesn’t equate to those in their family bloodline.

As to how Nick’s mental illness was being treated during his time in rehab, Taite tells TMZ there are “substandard treatment centers” that may not be supplying Nick with what he needs … “that’s the way the world works.”

As we previously reported … Nick was a patient at Alina Lodge — an addiction treatment center in New Jersey — and spoke on the “Dopey” podcast in 2016 about a moment where the staff refused to give him drugs … leading to him chucking a rock through a window to “show these mother f***ers that I’m crazy.”