Powdered opium

Finally, an analysis has shown that the remains of his supper left by the stable-lad contained an appreciable quantity of powdered opium, while the people at the house partook of the same dish on the same night without any ill effect.
Powdered opium is by no means tasteless. The flavour is not disagreeable, but it is perceptible. Were it mixed with any ordinary dish the eater would undoubtedly detect it and would probably eat no more. A curry was exactly the medium which would disguise this taste.