Lipinski's rule states that, in general, an orally active drug has no more than one violation of the following criteria:
* No more than 5 hydrogen bond donors (the total number of nitrogen–hydrogen and oxygen–hydrogen bonds)
* No more than 10 hydrogen bond acceptors (all nitrogen or oxygen atoms)
* A molecular mass less than 500 daltons
* A calculated octanol-water partition coefficient (Clog P) that does not exceed 5
Note that all numbers are multiples of five, which is the origin of the rule's name.
As with many other rules of thumb, such as Baldwins rules for ring closure, there are many exceptions'.