Well, my take on it is that Lochley came from a very strict family. Her father was in the military, if I remember correctly. She was rebelling hardcore. So, my guess is that her choice of drug would probably be something that allowed her to escape the discipline and control, something that allowed her to let go.
The first thing that comes to mind is something like ecstasy. It makes you a very social person, lovey, happy, touchy-feely. Some like to have sex while on it, but most people just like to touch and hug, etc.
Lochley coming from a background like the one she was in, perhaps there wasn't a lot of hugging and touching and outward displays of affection.
That's one idea.
The other idea is that she pretty much did whatever came along. If it was bad, she did it, totally going against anything and everything her father ever taught her or wanted for her. The worse the substance, the better it was for her rebellion.