On September 8, 2016, Ohio enacted House Bill 523 that allows a physician to prescribe medical marijuana. Ohio did not modify the OVI statute. In Dayton, you can be charged with OVI even if you are prescribed medical marijuana. Ohio calls a DUI an OVI, but it is really the same thing.
You can read the OVI statute in Ohio Revised Code, or ORC, section 4511.19, titled, “Operating vehicle under the influence of alcohol or drugs – OVI.” There are two ways you can violate the statute. One way is to drive a vehicle while you are under the influence of drugs or alcohol. The other way is to drive a vehicle with too much drugs or alcohol in your system no matter what observable effects it has on you.
This makes OVI similar to speeding. You do not have to do it knowingly. You only have to be over the limit. Even if you are under the limit, you can still be arrested and convicted of OVI. In some cases, no matter how little drugs or alcohol you consume, it can cause you to be under the influence.
Not all drugs have illegal limits. So far, Ohio has listed the following as having legal limits: alcohol, amphetamine, cocaine, cocaine metabolite, heroin, heroin metabolite, L.S.D., marihuana, marihuana metabolite, being under the influence with marihuana metabolite, methamphetamine, phencyclidine, salvia divinorum, and salvinorin A.

The legal limits for drugs in Dayton, Ohio for OVI / DUI are subject to division (K) of ORC 4511.19. Division (K) says that the legal limits do not apply for drugs if two conditions are met. First, that the person obtained the drugs from an authorized doctor’s prescription. And second, that the person took the medication as directed by the doctor.

Remember, this does not prevent you from being charged with OVI where the officer thinks that whatever amount of drugs you took caused you to be under the influence. So at this point, you might be wondering what it means to be under the influence.

The Ohio Jury Instruction given to jurors at a trial says “Under the influence” means that the defendant consumed some (alcohol) (drug of abuse) (combination of alcohol and a drug of abuse), whether mild or potent, in such a quantity, whether small or great, that it adversely affected and noticeably impaired the defendant’s actions, reaction, or mental processes under the circumstances then existing and deprived the defendant of that clearness of intellect and control of himself/herself which he/she would otherwise have possessed. The question is not how much (alcohol) (drug of abuse) (alcohol and a drug of abuse) would affect an ordinary person. The question is what effect did any (alcohol) (drug of abuse) (alcohol and a drug of abuse), consumed by the defendant, have on him/her at the time and place involved. If the consumption of (alcohol) (drug of abuse) (alcohol and a drug of abuse) so affected the nervous system, brain, or muscles of the defendant so as to impair, to a noticeable degree, his/her ability to operate the vehicle, then the defendant was under the influence.

Now you have a basic understanding of the OVI law in Dayton, Ohio. As it relates to the new medical marijuana law, it is now possible to have marijuana in your system and drive a car without fear of prosecution even if you are over the legal limit if you have a prescription for it and take it as directed. However, you are still exposed to the risk of being charged with an OVI if your medical marijuana causes you to be under the influence.