<unk>  is a phenomenon associated with the long term use of opioids  such as morphine, hydrocodone, oxycodone, and methadone.  Over time, individuals taking opioids can develop an increasing sensitivity to noxious stimuli, even evolving a painful response to previously non-noxious stimuli.  Some studies on animals have also demonstrated this effect occurring after only a single high dose of opioids.
Opioid-induced hyperalgesia
Neurogenic inflammation
Cardiovascular effects of cocaine
Fibromyalgia pathophysiology
Complex regional pain syndrome
Myofascial pain syndrome
Opioid withdrawal
Spinal autonomic dysreflexia