The difference is that marketing gives you a pretty steady ROI. Once the drug is developed, there is little to no risk involved in spending billions marketing a

The difference is that marketing gives you a pretty steady ROI. Once the drug is developed, there is little to no risk involved in spending billions marketing a drug. However, spending billions developing a drug without patent protection is a massive risk since drugs are easy to make but extremely hard to find. It would be trivial for a competitor to make the same drug at zero cost once its found to be effective. In this scenario researching drugs almost certainly has a negative ROI. Patents alter that calculation to make the endeavor worthwhile.