Is there any reason why someone would not want to use an intrathecal pain pump?

Complicated: Intrathecal drug delivery can be extremely helpful in many cases, severe cancer pain is a good example. Also much smaller doses delivered intrathecally can get even better results than oral doses. The downside is having the device refilled in the inherent risks of implants such as infection. These risks are rare.

Yes: Intrathecal pain pumps are a 'last resort' treatment for chronic intractable low back pain that is unresponsive to the more conventional therapies. The complications include but ate not limited to infection, catheter breakage, spinal headache, respiratory depression, and tolerance to increasing doses of medication.