The dilemma here being that you are choosing to work towards the distribution of a product that is known to have harmful and addictive effects. It's not a very challenging ethics problem though. The negative outcome is clearly defined, and agreed on by everyone.
This classic ethical question should be updated for 2017 to be something more akin to "Would you design a website for a publication known for spreading untrue information?", or "Would you do a project for a company which exploits indentured labor in the third world?".
The world we live in today is much more complex than the world of the 1990s, or even the 2000s. It's our job as visual communicators to not be ignorant of the effects our work has on the world.