Hi Betzbill I had severe diarrhea when I took Cymbalta. My doctor convinced me to keep trying it even though at that point the diarrhea had been ongoing for 10 days as he didn't think it was the Cymbalta causing it. Diarrhea is found among people who take Cymbalta, especially for people who are female, 60+ old , have been taking the drug for 1 month, also take medication Lyrica, and have Pain. This study is created by eHealthMe based on reports of 107,187 people who have side effects when taking Cymbalta from FDA, and is updated regularly. Along with its needed effects, duloxetine (the active ingredient contained in Cymbalta) may cause some unwanted effects. Although not all of these side effects may occur, if they do occur they may need medical attention. Find patient medical information for Cymbalta Oral on WebMD including its uses, side effects and safety, interactions, pictures, warnings and user ratings. Some of the most common Cymbalta side effects can include headaches, diarrhea, and insomnia. This eMedTV segment also takes an in-depth look at some of the more serious side effects of the drug, such as hallucinations and suicidal thoughts. Our Cymbalta Side Effects Drug Center provides a comprehensive view of available drug information on the potential side effects when taking this medication. This is not a complete list of side effects and others may occur. 11 Cymbalta Side Effects You Should Know About. You might have a really hard time quitting. I' m on cymbalta and i think its very good! Gives a lot of energy and i can stand the litle side effects i have, like increased sweating, and litle jaw tremor which is reducing by time. Find information about common, infrequent and rare side effects of Cymbalta Oral.