Who is they?  A Police Department?  They will ask you:

Have you ever used illegal drugs?
What illegal drugs have you used?
When was the first time you used ______?
When was the last time you used ______?
About how many times have you used ______?
Have you used illegal drugs within the last ____ years?
Other than what you already told me, have you used any illegal drugs?
Have you ever sold illegal drugs?
Have you ever bought illegal drugs?
What is the most you spend on drugs at a single buy?

You can expect questions along those lines.