How is 800 mg. prescription strength Motrin different from using OTC Motrin? Can I just take 4 OTC Motrin and achieve the same thing?

No. A normal motrin is 200mg and a prescription strength one is 800mg do not take four as that would be 1000mg which can be extremely dangerous. Always condult your doctor.
Also, I'm not sure if you are aware but, when using motrin you are at risk of a heart attack or a stroke if you use more than directed or for longer than directed.

No. A normal motrin is 200mg and a prescription strength one is 800mg do not take four as that would be 1000mg which can be extremely dangerous.
4 x 200 mg = 800 mg.

Ah.. that's a good point... sorry about that, my mind was somewhere else. Anyway, I still so not think its safe unless your doctor approves it.

The difference between prescription dosage and OTC dosage is to prevent self medications and overwhelming your system and having bad reactions due to drug interaction, and side effects that must be monitored and addressed by a physician. Low doses are relatively safe, as opposed to higher doses. If you notice on any drug bottle there is a recommended dosage that limits daily intake/usage of this drug. And when you exceed it for a period they tell you to see a doctor when symptoms persist.

Mainly, you shouldn't take a higher dosage unless a doctor recommends it. Or you wouldn't be following the recommended dosages that are safe. As far a chemical difference, NO, but higher doses entail higher risks, and a lot of supervision.

That's the difference, a doctors recommendation, based on knowledge, or you just wanting to save money and feel better. Also I note the prescription is limited to a few days, and the doctor re evaluates your condition.