**1. Introduction**

Chronic pain is one of the most prevalent and disabling conditions in the clinical setting with both physical and psychological symptoms [1]. In the past three decades, there has been a better understanding of the underlying pathophysiological mechanisms that cause chronic pain, yet it still remains a significant problem. Multiple levels of the nervous system with multiple neurotransmitters are involved in pain transmission. Therefore, it is not so easy to plan effective pharmacological therapy for chronic pain and pain treatment often involves the use of one or a combination of agents with analgesic action [2]. Chronic pain may be nociceptive or neuropathic. Nociceptive pain usually is treated with anti‐inflam‐ matory or analgesic medications. Neuropathic pain typically is treated with medications

© 2017 The Author(s). Licensee InTech. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

that influence neurotransmitters (e.g., antidepressants, antiepileptic drugs), and treatment with opioids is reserved for patients with refractory neuropathic pain. There are no truly effective medicines for certain types of pain; thus, a better understanding of the existing ones [opioids: methadone and tramadol; antidepressants: tricyclic antidepressants (TCAs), selective serotonin reuptake inhibitors (SSRIs), serotonin‐noradrenalin reuptake inhibitors (SNRIs); anticonvulsants: gabapentin and pregabalin] or the search for new or perhaps the oldest form of medicine (cannabis) is needed.

The usual approach is to start with a nonopioid analgesic such as a nonsteroidal anti‐inflam‐ matory drug (NSAID) or acetaminophen for mild‐to‐moderate pain. If this is inadequate, the next step may be to add an antidepressant. If there is a component of neuropathic pain, then a trial of one of the anticonvulsant analgesic agents could be the option. If these steps are inadequate, then an opioid analgesic may be added. In an individual patient, one or several mechanisms may be at play in the etiology of the pain and more than one agent may be neces‐ sary for pain control; thus, it may be appropriate to use a combination of agents with different mechanisms of action in an effort to obtain adequate pain control [3].

This chapter focuses on pharmacotherapeutic options for patients with chronic, no cancer pain and possible drug‐drug interactions that can result from a combined therapy.
