These have been tough times for meds for mental illness, with an array of health concerns coming to the surface. Now, on another front, Eli Lilly (NYSE:LLY) has confirmed that it sent a warning to physicians concerning its blockbuster antipsychotic medication, Zyprexa. That warning had to do with a higher incidence of stroke in elderly users suffering from dementia.

The Wall Street Journal broke the news early today. It echoes Johnson & Johnson's (NYSE:JNJ) warning on its own schizophrenia drug, Risperdal, back in April. If Lilly investors are feeling nervous, it's probably because Zyprexa represented $4.3 billion in sales this past year, or one-third of total sales. This piece of news is hardly heartening, considering Zyprexa has also faced several patent challenges.

However, before getting too upset, the upside is that Zyprexa isn't actually approved by the FDA for use in the kind of dementia that elderly people often suffer from, such as that related to Alzheimer's.

It's not unusual for doctors to prescribe medications approved for one ailment to treat others -- even if the FDA hasn't approved them for that illness. Zyprexa is approved for bipolar disorder and schizophrenia. Sometimes, it's the only game in town, and if it works, it works.

This is certainly not high on the list of news items Lilly's welcoming. Just a few weeks ago, a public relations snafu occurred regarding the company's upcoming antidepressant, Cymbalta. It came to light that one of the healthy patients in its study (a test subject for the physical safety of higher-than-normal doses, not related to its effectiveness for depression) committed suicide. Though Lilly denied that the suicide had any association with Cymbalta and it still believes the medication will gain approval, it wasn't the kind of attention the drug maker wanted.

According to Reuters, prescriptions for dementia might represent 2% of sales, but it seems difficult to imagine the company would know for sure -- after all, this is the type of prescribing that would fly under the radar. However, Lilly may have been facing increasing danger that it would lose this particular subset of users anyway.

Why? Forest Laboratories (NYSE:FRX) is currently launching its high-profile Alzheimer's drug, Namenda. Namenda represents hope for patients that have moderate-to-severe forms of the disease, which seems like the demographic that could have taken Zyprexa.

Lilly shares were down only marginally in today's trading session, and that seems about right. It's hard to tell what impact this -- or Namenda -- will have on what elderly patients with dementia will be prescribed. For now, when it comes to a new blockbuster candidate, all eyes turn to Cymbalta.

Shopping for stocks? Do news developments like this one make you think you'd like to avoid pharmaceutical stocks? Consider checking out Motley Fool Stock Advisor .

Alyce Lomax does not own shares of any companies mentioned.