Growth stocks often don't come cheap, especially when their prospects look great, as is the case with Eli Lilly (LLY 1.09%). It is the most valuable healthcare company in the world, with a market cap of around $800 billion. And yet it may still not be too late to invest in it.The company's dominance in the GLP-1 drug market makes it a promising long-term investment to hang on to. Last year, its sales rose by 32%, but there could be even more growth on the horizon.Eli Lilly is going after compounding pharmac ...