Dre is being sued by Dr. Charles Sophy, a psychiatrist who says he provided Dre and his ex-wife Nicole therapy and marriage counseling sessions during their union, before staying on to act as a mediator during their divorce.

According to the lawsuit, obtained by TMZ, Sophy claims Dre started bombarding him with abusive and threatening text messages 14 months after the divorce was finalized.

Sophy claims Dre is falsely accusing him of encouraging a third party to bad-mouth Dre in the media during the divorce proceedings ... and he says the threats reached a head when Dre sent associates disguised as FBI agents to his gated community to track him down.

In the docs, Sophy claims Dre's called him a "bitch" and a "piece of s***" over text and threatened to "make you pay for that."

Sophy claims Dre started harassing him over text in February 2023 ... and shortly after, Sophy says Dre hired some men to impersonate FBI agents in order to gain access to his home to threaten his physical safety and send a message.

Since the alleged incident, Sophy claims he's had to beef up security at home and he doesn't leave the house unless he's wearing a bulletproof vest and cap.

Sophy is suing Dre for $10 million ... and he also wants an order requiring Dre to stay 100 yards away from him.

Howard King, Dr. Dre's lawyer tells TMZ ... "Dr. Sophy filed his suit only after he failed to pressure Mr. Young into dropping efforts to get Dr. Sophy punished for dereliction of duties and incredible incompetence. These claims are set forth in detail in a confidential complaint Mr. Young filed in 2023 with the Osteopathic Medical Board of California."

He continues ... "That complaint seeks revocation of Dr. Sophy’s license to provide mental health counseling to needy patients. In gross violation of all applicable standards of care, Dr. Sophy inserted himself into a contentious divorce while he simultaneously 'treated' not only Mr. and Mrs. Young, but their children."

King adds ... "He was terminated when it was revealed that he was encouraging one of their children to take sides against Mr. Young, even encouraging his son to go to the press with false allegations in order to force a financial settlement that he recommended. Dr. Sophy has consistently rebuffed Medical Board attempts to investigate these claims, but has now filed this desperate suit while the noose of the Medical Board is tightening."