The three have pleaded not guilty to providing the former Playboy model with excessive drugs while knowing she was an addict.
The judge then instructed the jurors on the law that will govern their decisions, telling them not to let sympathy or public opinion sway their verdicts. He also said a conspiracy conviction must only be reached if the defendants agreed to commit the alleged crimes.
The closing arguments are aimed at swaying jurors who will deliberate on several charges against Stern, Kapoor and Eroshevich.
A judge has already thrown out some of the charges, citing insufficient evidence.
At issue is whether the former model was given excessive drugs, whether the defendants gave her fake prescriptions and whether she was actually a drug addict.
The three defense attorneys are expected to plead for the doctors and for Stern to be acquitted, claiming that they cared for Smith and were trying to help her with medical concerns.
The three are not charged in Smith's 2007 overdose death, which was ruled accidental.
The case could go to the jury by Thursday. The defendants face unspecified fines and prison sentences if convicted.
The Associated Press contributed to this report.