Gregory Thompson earlier said the drugs prescribed for Smith would be effective "if you were going to kill someone."
The judge's caution also applied to a pharmacist who once described the drugs ordered by defendant Dr. Khristine Eroshevich as "pharmaceutical suicide."
On Tuesday, Thompson was questioned about a conversation he allegedly had with Eroshevich.
Thompson said he expressed shock after learning the list of drugs the doctor was administering to Smith and urged her to take Smith to a rehab center in the Caribbean.
They are not charged in her 2007 death from an overdose.
The Associated Press contributed to this report.