It could affect up to a million people.
They have discovered that people taking both the antidepressant Paxil and the cholesterol-lowering drug Pravachol could get unexpected spikes in their blood sugar.
Researchers were surprised to find the link, because neither drug alone causes a similar problem.
But doctors from Stanford University School of Medicine, Vanderbilt University, and Harvard Medical School found it by looking at the Food And Drug Administration's database of "adverse events," or bad reactions.
Doctors are encouraged to report the adverse events, however, some physicians have questioned the usefulness of the databases.
After finding this link, the researchers now wonder how many other hidden drug conflicts could be out there.
They says the glucose spikes are especially dangerous for people who are already diabetic.
If you take those drugs, be sure to check with your doctor.
