How many poisons are in cigarrettes?

It's impossible to answer this precisely.

You've probably seen some kind of scare tactic anti-smoking Propaganda claiming there are over some large number of poisons in a cigar, and that's probably true... for a suitable definition of "poison." However, it's probably also true of peaches, yoghurt, and spring water (or, for that matter, anything else).

The issue is this: we have the technology to detect chemicals at extremely trace amounts... it's routine to be able to detect parts per billion, which, to put it into perspective, represents less than a tenth of an ounce in an Olympic-size swimming pool, and there are techniques that make detecting parts per trillionnot particularly difficult.

When you go looking for quantities this small, it turns out you find all sorts of odd stuff everywhere. Pesticides, toxins naturally produced in tiny amounts by many living cells, heavy metal ions... and they're in everything.