But the court overruled the prosecution and ordered a trial.
Wearing a dark grey business suit and a facemask, Lee remained tight-lipped as he entered the Seoul Central District Court, skipping questions from reporters.
In court, prosecutors demanded a larger fine of 70 million won, Yonhap news agency reported.
Lee’s lawyers maintain the substance was administered for medical reasons.
“It was prescribed in accordance with medical procedure by a doctor during Lee’s treatment,” they said in a statement.
Samsung Electronics declined to comment.
The firm is the flagship subsidiary of the giant Samsung group, by far the largest of the family-controlled empires known as chaebols that dominate business in South Korea, the world’s 12th largest economy.
Lee became the conglomerate’s de facto leader following the death of his father last year.
Two months ago he was released early from a two and a half year prison term for bribery, embezzlement and other offences in connection with the corruption scandal that brought down ex-South Korean president Park Geun-hye.
The early release was seen as the latest example of South Korea freeing on economic grounds business leaders imprisoned for corruption or tax evasion.
Samsung Electronics subsequently announced a giant $205-billion investment plan, three-quarters of it planned for the South.
But Lee remains on trial on separate accusations of manipulating a takeover to smooth his succession at the top of the Samsung group—the same controversy over which he was said to have sought help from Park.