"I only put four or five drops into her tea," the unidentified man told the court in Castrop-Rauxel as he admitted to the crime.
In August 2014, he was playing on his games console with a friend one evening when his then girlfriend arrived home.
The man then gave her a sedative in her tea so he could continue playing video games, the 'Westdeutsche Allgemeine Zeitung' reported.
The woman slept until midday the following day after drinking the drugged tea.
The boyfriend admitted what he had done the day after the crime, according to 'The Local'.
"Your girlfriend slept long and deeply, which didn't harm her, but this is certainly a premeditated bodily harm," the judge said as he ordered the man to pay a 500 Euros fine.