Eli Lilly (LLY -0.14%) is the most valuable healthcare stock in the world, with a market capitalization of nearly $700 billion. But in recent weeks, its share price has been falling. And now the stock is down over 20% from its 52-week high of $972.53. Could this be a great time to add the high-powered healthcare stock to your portfolio?Why is Eli Lilly stock struggling of late?Eli Lilly has been a fantastic growth stock to own in recent years. Entering trading this week, its five-year returns have totaled m ...