The Food and Drug Administration warned Thursday that diabetes drugs might be elevating the rate of pancreatic cancer.

Investors shouldn't be surprised. Nor particularly worried.

We've known for years that GLP-1 drugs increase the likelihood of pancreatitis. I wrote about an FDA warning about Byetta nearly five years ago.

Last month, a study in JAMA Internal Medicine showed that Byetta -- which is now owned by AstraZeneca (NYSE:AZN) and Bristol-Myers Squibb (NYSE:BMY) after they bought Amylin Pharmaceuticals -- and Merck's (NYSE:MRK) Januvia double the rate of pancreatitis.

Januvia is a DPP-4 inhibitor, but GLP-1 drugs and DPP-4 inhibitors work on the same pathway to lower glucose -- DPP-4 inhibits GLP-1 activity -- so it's not surprising that they would have the same effect on the pancreas.

The latest warning comes from unpublished data shared with the FDA that showed inflammation and pre-cancerous cellular changes in pancreas biopsies from patients taking DPP-4 inhibitors and GLP-1 drugs.

Since it's believed to be a class effect, the FDA warning extends beyond Januvia and Byetta to all the DPP-4 inhibitors and GLP-1 drugs: Novo Nordisk's (NYSE:NVO) Victoza, Bristol and Astra's Onglyza, Takeda's Nesina, Eli Lilly (NYSE:LLY) and Boehringer Ingelheim's Tradjenta, and their combination products.

If the drugs were pulled from the market, it would be devastating to the companies, especially Merck since Jaunvia is a multibillion-dollar blockbuster. But investors shouldn't worry quite yet. This is very preliminary data and "pre-cancerous cellular changes" doesn't necessarily lead to a large increase in the rate of cancer.

It seems possible -- dare I say likely -- that the FDA will find that the drugs cause a small increase in the rate of pancreatic cancer, but that the benefits outweigh the increased risk. The agency will slap a warning on the drugs, and we'll be back to business as usual.