Scientists at the Massachusetts General Hospital have combined a normally inactive lidocaine derivative with capsaicin, the ‘heat’-generating ingredient in chili peppers, to produce pain-specific local anesthesia. When injected into rats, this combination completely blocked pain without interfering with either motor function or sensitivity to non-painful stimuli.
This technique could revolutionize pain management, as it specifically targets pain-sensing neurons. Current local anesthetics block all neurons, not just pain-sensing ones, and produce dramatic side effects such as temporary paralysis and complete numbness. 
This means that using this drug you are still aware of touch while you are unaware of pain. A lot new applications could result if the new method is validated in humans (hopefully in 2 or 3 years).
As reposrted in Nature , rats given an injection of the anaesthetic were able to tolerate more heat than usual, while moving around normally. Then, they tried injecting the anesthetic near the sciatic nerve of the rats and pricked their paws with nylon probes. The animals seemed to ignore the painful prick, but continued to move normally and responded to other stimuli.
Researcher Professor Clifford Woolf, of Harvard Medical School and Massachusetts General Hospital in Boston in the US, said: ‘We’re optimistic that this method will eventually be applied to humans and change our experience during procedures ranging from knee surgery to tooth extractions.
‘Eventually this method could completely transform surgical and post-surgical analgesia, allowing patients to remain fully alert without experiencing pain or paralysis. ‘In fact, the possibilities seem endless. I could even imagine using this method to treat itch, as itch-sensitive neurons fall into the same group as pain-sensing ones.’
In time, it may be possible to package it in pill form, rather than giving it as an injection. There are, however, several hurdles to be crossed before the technique can be tested on human patients. Scientists will have to find a way of removing the temporary burning sensation associated with the use of capsaicin, as well as prolonging the pain-relieving effect of the drug.
 News release, Massachusetts General Hospital and Harvard Medical School. (http://web.med.harvard.edu/sites/RELEASES/html/Oct07Pain.html)
 Nature, Oct. 4, 2007
“Inihibition of nociceptors by TRPV1-mediated entry of impermeant sodium channel blockers”
Alexander M. Binshtok (1), Bruce P. Bean (2), and Clifford J. Woolf (1)