Final answer:
Ephedrine, pseudoephedrine, and phenylpropanolamine are drugs that are required to be behind the counter. They are commonly used as nasal/sinus decongestants and stimulants. These drugs are also used as precursor chemicals in the illegal production of methamphetamine.
Step-by-step explanation:
In the United States, ephedrine, pseudoephedrine, and phenylpropanolamine are drugs that are required to be behind the counter. These drugs are commonly used as nasal/sinus decongestants and stimulants. They are often found in over-the-counter preparations, either as a single ingredient or in combination with other medications like antihistamines and pain relievers.
It is important to note that these drugs are also used as precursor chemicals in the illegal production of methamphetamine, which is why they are regulated and restricted.