NEW YORK ( TheStreet) -- Shares of Eli Lilly ( LLY), which are down more than 15% over the past six months, are still under pressure following a recent downgrade from Jefferies analyst Jeffrey Holdford. Not only was the stock reduced to underperform from hold but Holdford cut the price of the stock from $49 per share to $40, which suggests a possible 20% downside from current levels.Among other things, Holdford cited Lilly's pipeline, which is seen as weak and able to support neither the company's current dividend nor future cash flow allocations. Truth be told, while I haven't been Lilly's biggest fan, I don't subscribe to this recent assessment. It's not that I disagree with Holdford's concerns, they're just not new. As noted, with the stock already down more than 15% since April, I believe Lilly's poor pipeline situation, which has long been an unwanted stigma, has already taken its toll. That said, I don't want to make light of what can potentially hinder the company's growth. Not unlike, say, Pfizer ( PFE) or Merck ( MRK), Lilly has considerable exposure to what is known in Big Pharma as the "patent cliff." For instance, as the 2013 winds down, Lilly's top-selling antidepressant drug Cymbalta, which accounts for more than 25% of the company's revenue, goes off patent. What this means is that generic rivals to Cymbalta can then become worthwhile threats. But that's just one of several concerns. Shortly after Cymbalta goes off patent, Evista, which is Lilly's strong breast cancer reduction drug, will follow. Given that Evista generates close to $1 billion in revenue, this means that almost two-thirds of Lilly's 2013 revenue will be -- essentially -- up for grabs within a few years. Again, this patent-cliff situation was well known prior to the start of the year. But the stock still managed -- at one point -- to post gains of close to 22%. The Street understood that Lilly was not alone. And drug giants are known to overcome pipeline fears. It goes with the territory. Shares of Merck, for instance, are up more than 16%, even after the company lost the patent to Singulair, which is its top-selling asthma drug.