Normally in this type of case, whatever the police say at the time of the arrest or whatever is on an initial ticket that they issue, the charge is not officially made until the crime lab report confirms the nature of the substance found in the defendant's possession. That is normally this would not be an issue because the prosecutor would be waiting for and working from the crime lab report even if the police issued a citation that on its face identified a different drug.
But let's say that this was be a charge brought on an information, and that the information misidentified the controlled substance. In the absence of a showing of prejudice to the substantive rights of the defendant, amendment is permissible.

