Pethidine is indicated for the treatment of moderate to severe pain, and is delivered as a hydrochloride salt in tablets, as a syrup, or by intramuscular, subcutaneous or intravenous injection. For much of the 20th century, pethidine was the opioid of choice for many physicians; in 1975 60% of doctors prescribed it for acute pain and 22% for chronic severe pain. Compared with morphine, pethidine was thought to be safer, carry a lower risk of addiction and to be superior in treating the pain associated with biliary spasm or renal colic due to its putative anticholinergic effects. It was later discovered that these were all myths and that it carried an at least equal risk of addiction, possessed no advantageous effects on biliary spasm or renal colic compared to other opioids and that, due to its toxic metabolite, norpethidine, it was more toxic than other opioids, especially during long-term use.