For a free iPhone application, Skyscape Medical Resources provides a lot.  Just make sure you have Internet access when you use it. Having a medical degree wouldn't hurt either. 

The application provides a prescription calculator that assesses the effects and dosage of drugs you are taking. Skyscrape also serves as a resource that describes various diseases and treatments, as well as a medical calculator that even monitors your calorie intake. 

Although the app provides a wealth of medical knowledge -- including a glossary of terms and links to related ailments -- Skyscape isn't for everybody. It is specifically designed as a resource for medical professionals, which means the rest of us likely won't understand what to do with all the information. 

There are other annoyances. Without reliable Internet access, Skyscape doesn't work. The app also suffers from some functionality issues. Archimedes, the medical calculator, is clunky and might be missing some buttons. It is important, for instance, for a calculator to have all of its buttons. 

Skyscape also lets you download additional resources. But they come at a premium -- some as high as $49.99 or more for medical books and apps.

It’s hard to quibble because app is free, but don’t expect a lot of ease of use.