In actual fact, the answer is no. I think that drug recognition experts will testify before you, at which time they will be able to give you a much more definite answer.
The problem is that there are seven families of drugs. There are thousands of drugs, many of which are illegal, and their effects on any given individual can depend on all kinds of factors. Drugs don't act like alcohol. Moreover, if you add a small amount of alcohol to some drugs, the effects can be quite different.
The prosecutions will be based on observations leading to an individual's arrest. The arrest is based on grounds the police might have had to suspect the individual had consumed drugs, as well as on the results of roadside tests carried out, and on the expert's assessment, which is then confirmed by the tests. If the tests do not confirm that the individual took cocaine when the expert said he took cocaine, that will be the end of it, and there will be no prosecution. That sequence has already been approved by courts in Canada as being sufficiently convincing to incriminate the individual beyond any reasonable doubt.