Possible Clues:

• Slimy
• Too slippery and slimy to grasp
• Hard to catch, in a way
• Wriggling and slippery
• Difficult to get hold of drug, see?
• Wriggly and slippery, e.g.
• Long and squirmy
• Lamprey-like
• Tough to catch
• Wet and slithery?