If your dentist prescribes a special toothpaste for you to use, he or she may want you to use it at night after you’ve already brushed with another toothpaste. That way the prescription grade product can have maximum contact with your already clean teeth and work as designed.
Most prescription toothpastes contain a higher concentration of fluoride, which is why they’re sold behind the counter at pharmacies.
As with everyday toothpastes, you only need to use an amount about the size of a pea when you’re brushing with a prescription grade gel. Any more than that, and you could accidentally swallow too much fluoride and get an upset stomach.