The first effective local anaesthetic was cocaine.
The first local anesthetic used in dentistry was Cocaine, introduced as an anesthetic by Carl Koller (1857-1944) in 1884. Researchers soon began working on a non-addictive substitute for Cocaine, and as a result German Chemist, Alfred Einkorn introduced Novocain in 1905. Alfred Einkorn was researching an easy-to-use and safe local anesthesia to use on soldiers during wartime. He refined the chemical procaine until it was more effective, and named the new product Novocain. Novocain never became popular for military use; however, it did become popular as an anesthetic among dentists. But Novocain is a brand name so more often you will find your dentist pulling out the procaine before pulling out yer gnashers.
Sizzle, you might be referring to opioids rather than opiates. Opioids are largely used for pain relief (such as morphene which is an opioid alkaloid) and are as such more suited as an analgesic rather than anesthetic. I think the use may be cointraverisl though as opioids have dependance and withdrawal issues.