extra shots

Hello everybody.
A man wants a girl to go to bed with him. So, he plies her with drink. And:
"He slipped some extra shots into her drinks".
What are shots? Pills? Drug?
Thank you very much
Chiarel

Shots in this context are usually hard liquor, such as vodka or whiskey. He increased the alcohol content of her drinks by adding more of whatever hard liquor was the basis of the drink.

A "shot" is a measure of alcohol. If he added "extra shots" to her drinks, he added more alcohol than the drink usually had, so that she would get drunk.

If she is used to having a certain number of drinks without getting drunk, and she drinks the same number with the extra alcohol, she will get drunk without intending to.

Added: Cross-posted with JamesM. I'm slow.

Thank you very much, James and Cagey!