Under the influence means that you consumed some alcohol, drugs, or a combination of the two, whether mild or potent, in such a quantity, whether small or great, that it adversely affected and noticeably impaired your actions, reaction, or mental processes under the circumstances then existing and deprived you of that clearness of intellect and control of yourself that you would otherwise have possessed.
The question is not how much alcohol or drugs would affect an ordinary person. The question is what effect did any alcohol or drugs, consumed by you; have on you at the time and place involved. If the consumption of alcohol or drugs so affected your nervous system, brain, or muscles so as to impair, to a noticeable degree, your ability to operate the vehicle, then you were under the influence.
Most people do not understand that in Ohio there are usually two OVI charges filed against a driver. One is being under the influence of drugs or alcohol. The other is driving a car and having an unlawful amount of drugs or alcohol in your body based on a test result. To be convicted of being over the limit you do not have to be drunk or driving dangerously. Much like speeding, you just have to be over the limit. The state has to prove impaired driving ability versus actual impaired driving. For instance, you can be stopped for a tail light out and still be convicted of DUI.
If you are under 21 years old the prohibited alcohol limit is 0.02 BAC. This might be less than one beer in most cases. This is very different from being under the influence. In fact, most of the SFSTs will not work in this case because they are only used to determine when a person has a chance of being over the limit of 0.08 BAC. However, the standard to arrest for this offense is much lower than for someone over 21 years old. Usually finding out that someone is under 21, a little bad driving, an odor of alcohol and admission of drinking is enough to support an arrest.