The Iron Rule-out of Mental Health Symptoms: "It's never the marijuana"

It's been a while since I heard it, but a patient today uttered the immortal phrase "It's not the marijuana" because (like Dr. House's Lupus): "It's never the marijuana." Trouble sleeping? Maybe it's the coffee, or the late night TV, or the wife, or the light, or the diet, or the depression. It can be any of a dozen things. What about the 2 joints a day? Oh? Sorry, it can never be the marijuana: "I'll change anything else, but I won't change that. It's not the marijuana." Right.