The penalties for driving under the influence of either drugs or alcohol are very similar, but the police procedure involved in making this determination are very different.
In the case of drugs, the arresting officer needs to bring a drug recognition expert to the scene to aid in making a determination. For the state to prove its case, you must be taken to a hospital to provide a blood sample.
The critical thing to know is that you can legally refuse to give a blood sample; in that case the police need to obtain a warrant. If they can’t get one, if they go ahead and get a blood sample anyway it is not admissible in court.