Related Clues:

• Dennis the Menace, for one
• It's taken in for treatment
• Hanger-on
• Unwelcome guest
• Bothersome person
• Drug unit
• Tiresome sort
• Adamant ant?
• Tab
• Dosage, maybe
• Thorn in one's side
• Grumpy person
• Aphid, to a gardener
• Exterminator's target
• Termite, e.g.