i cant answer yes or no to a question which , when stated, means you completley misunderstand what is going on.
1) you take a drug
2) it is sometimes metabolized into a chemical and excreted. the new chemical obviously is a known breakdown product of the drug, and identifying the breakdown product means you have also identified the drug
3) or it is excreted unchanged
4) you calculate the volume of the water you are assaying
5) you determine the concentration of the drug
6) you find out how much you must have star6ted with.
FYI no laboratories on the hudson use several metric tons of cocaine. no, not even super secret research laboratories owned by neo nazi zionist neocons. these are locaed in tulsa