Chronic pain is treated in an individual suffering from chronic pain by administering to the individual an amount of a therapeutic containing a glycine receptor agonist such as D-cycloserine or a GlyT-1 glycine transporter antagonist such as sarcosine in an amount effective to treat the chronic pain. The therapeutic may also contain a secondary analgesic such as opiates, NSAIDs or cox-2 inhibitors. The analgesic can be formulated in a pharmaceutical composition in the form of an injectable solution that contains at least two different analgesics, at least one of the analgesics of which is a glycine receptor agonist or a GlyT-1 glycine transporter antagonist. Suitable pharmaceutical compositions contain D-cycloserine and/or sarcosine, optionally in combination with opiates, NSAIDs or cox-2 inhibitors.