The corks on the potion flask are an indicator of the potion grade, unlike ki pills whose grade can be identified by their smell.
A low-grade potion has a brown cork
A mid-grade potion has a grey cork
A high-grade potion has a black cork
An elixir which is the highest rank a potion can reach has a white cork. That is the same for every potion
A low-grade health potion/pill can heal minor injuries such as little cuts and bruises.
A mid-grade health potion/pill can heal the same thing that the low-grade one can and also heal minor illnesses like colds and things like that.
A high-grade health potion/pill can heal all the things that the mid-grade one can and it can heal large wounds, broken bones, and some deadly illnesses.
An elixir is the Apex of a potion or a pill, it is the highest grade and when it comes to health potion, it can heal everything. However, up to this day, nobody has been able to make one, making it nothing more than a myth.
OI is the abbreviation of Over Intake. It happens when a person takes multiple different potions or pills at the same time or in too short intervals. That will result in experiencing drowsiness, vomiting, dizziness, and sometimes various other symptoms.
A low-grade energy potion/pill recovers a quarter of a person's energy
A mid-grade energy potion/pill recovers half of a person's energy
A high-grade energy potion/pill recovers a person's energy fully.
According to legends, an elixir can recover a person's energy fully and put them in a state where they constantly recover lost energy, in other words, grants them a whole other 100% of energy.