I would also ask my pharmacist after I checked with the drug manufacturer to see what info came out of the FDA trials. If you don't feel comfortable with info they gave you that you think applies to his situation, then discuss that with the doctor.
btw, most side effects go away with time and people don't get most of the side effects anyway, but everyone is different.
Cymbalta is in the snri class of meds. These have been associated with liver disease, so if he has any problems with the liver I'd consider this. It has been approved for chronic pain, but it doesn't do anything about the cause of the pain, it just makes the patient not care as much. This class of meds targets ot only serotonin receptors but also norepinephrine receptors, so if he is an anxiety sufferer this drug can make it worse. This class of drugs is very hard to stop taking. Keep in mind that psychiatrists have the most experience with antidepressants, and if you find a good one they can be good at helping people slowly stop taking them if the desire to stop arises, but other doctors are not usually good at this. Also consider that geriatric medicine often is geared more to sedating a patient than treating them by some doctors especially if the patient if in a nursing home. So the balance is, does he have full control of his mental faculties so he can make his own decisions? Has the doctor given full disclosure about the problems related to this med? Has sufficient attempt been made to find the cause of and treat his condition, including anything he is doing that might be making the problem worse that can be helped by changes in diet and lifestyle? If he believes everything has been tried and tried again and a treatment can't be found, then this med or some other pain suppression med might be the best he can do.