“There’s many a slip ‘twixt cup and lip,” as the saying goes. One small letter can make a world of differences and there are Sunday magazine comic strip writers who have made their livings out of this fact.
Always make sure you don’t mix up prescription and proscription. They’re different prepositions, and different propositions entirely! One will help you feel better whereas the other probably won’t.
Always better to be prescribed that proscribed. 🙂