No drug where a 2% difference matters can be administered outside of a monitored hospital setting. There are too many variables that affect the drug uptake far more than 2%, such as body weight (100 pound person will have 3x the drug dosage of a 300 pound person), drug absorption (based on body chemistry, other food eaten, etc.) and the actual intake dosage itself (Eye drops, for example, can have a 500-fold variance in how much actually gets administered). That's why over-the-counter drugs have to have very high therapeutic index. https://en.wikipedia.org/wiki/Therapeutic_index