Drugs are just molecules that are small enough to interact with the cells in your body. We've discovered a lot of them: 67 million unique substances, according to the American Chemical Society. But this is only about one tenth of one percent of the potential drugs out there, so we've definitely got some work to do.
To estimate how many drugs have yet to be discovered, researchers from the University of Berne in Switzerland tried to figure out just how many small molecules could possibly exist within the constrains of physical and chemical laws. For example, some molecular shapes are impossible. Some combinations of atoms are impossible. And some molecules are just too big to be effective at interacting with other molecules in our bodies.
If you ask a computer to figure out all the molecules that are left, though, you get a very very large number: something in the neighborhood of one novemdecillion, which is equal to one million billion thousand thousand billion thousand billion million thousand billion, or a one followed by 60 zeros in a row. For the record, this is a somewhat larger number than the total number of stars estimated to exist in the known universe.
That's great. Really, it's great, we like large numbers, but how is this at all helpful? Well, by defining the complete space in which new drugs can be found, it might be possible to use computer modeling to suggest new molecules to synthesize and predict what they'll be able to do based on other known molecules with similar structures. Already, the research team thinks they've found a molecular analogue of nicotine this way, and they think that more drugs that do helpful things to the central nervous system may soon follow.