I can attempt to increase the demand of our product by damaging the reputation of the Sun Yee On.

Previously, I came to the conclusion that killing their end-users via their own product would probably make the biggest dent in their reputation.

The easiest way to create deadly cocaine would be to target the cocaine that goes onto the streets rather than the high-quality cocaine that goes to the rich. The stuff that goes to the rich is definitely double- and triple-checked.

Powdered ricin, perfect. It's incredibly deadly, but it won't kill the user instantly. This way, it will be difficult to detect which batches are toxic.

Moreover, the tiniest amount of ricin will be lethal. Even an amount smaller than the period at the end of this sentence will be lethal.