Bonds' attorney Allen Ruby acknowledged his client took two designer steroids, but said he did so unwittingly.
"I know that doesn't make a great story," Ruby said, "But that's what happened."
But a federal prosecutor told the jury it's "ridiculous and unbelievable" that Bonds would believe his personal trainer was giving him flax seed oil and arthritis cream.
Assistant U.S. Attorney Matt Parrella started the day by saying Bonds lied to the grand jury even though the government promised not to prosecute him for drug use if he testified truthfully.
"All he had to do was tell the truth, Parrella said. "That's all, but he couldn't do it."
Bonds has pleaded not guilty to charges of obstruction and lying to a grand jury.
Greg Anderson, Bonds' personal trainer, was taken to jail Tuesday after he told U.S. District Judge Susan Illston he was refusing to testify against Bonds, whom he grew up with in San Mateo County.
The Associated Press contributed to this report.
