It's good to see that Vertex Pharmaceuticals has rewarded shareholders with a total shareholder return of 42% in the last twelve months. That's better than the annualised return of 12% over half a decade, implying that the company is doing better recently. Someone with an optimistic perspective could view the recent improvement in TSR as indicating that the business itself is getting better with time. While it is well worth considering the different impacts that market conditions can have on the share price, there are other factors that are even more important. Consider risks, for instance. Every company has them, and we've spotted 1 warning sign for Vertex Pharmaceuticals you should know about.