In just four lines, the speaker describes a drug user's comedown, or at least a moment when the drug no longer delivers what it once did. The title points to meth, and the poem admits it directly: it is "being little pleasure now." That phrase is flat and tired, as if the speaker has stopped pretending.
What's striking is what happens next. Instead of a dramatic crash, the speaker becomes "very homely," which suggests plain, humble, stripped of glamour. Then comes a quiet act: they "sing a thin thought." The word "thin" makes the song feel fragile and barely there, though the fact that they still sing at all gives it a small, stubborn tenderness.
The opening phrase, "a din of light," mixes sound and sight in a way that feels overstimulated, like a brightness that is almost noisy. Against that, the ending is hushed. The mood is weary and exposed, with a flicker of honesty rather than self-pity.