Ventolin is an asthma inhaler, which is the medicine she's referring to.
The song is about how some individual is making the narrator have an asthma attack, but is also the one that hid the narrator's medicine.
It's also probably a metaphor for a relationship, in which the individual caused the person to get into this "state" and has hid his/her "medicine", which is getting out of the relationship.
Ventolin is an asthma inhaler, which is the medicine she's referring to.
The song is about how some individual is making the narrator have an asthma attack, but is also the one that hid the narrator's medicine.
It's also probably a metaphor for a relationship, in which the individual caused the person to get into this "state" and has hid his/her "medicine", which is getting out of the relationship.