Medicine is sold in two ways:
- "Prescription drugs" require a prescription from a doctor. You can't buy them unless you have this. They're only sold at drug stores.
- "Over-the-counter drugs" don't require a prescription. You can buy them at a drug store or sometimes even at grocery stores, convenience stores, etc.
For over-the-counter drugs, you can say that they are "sold over the counter":
A: Is it sold over the counter?
B: No, it's a prescription drug.