Sans has definitely done stuff harder than weed as well, but keeping it to marijuana has been one of his few instances of self control. Maybe it's the scientist in him. It's a calculated choice - the lowest risk for the most effect. And hey, he's gotta have some dignity.

Not that he's keeping most of it right now.

"Not sure you're gunna enjoy that, kid," he slurs unhappily, wrapping an arm around himself a bit more tightly. Even companionable silence is going to be a bit much for him at the moment.