Promethazine enhances the analgesic effect of opioids.
The myth that promethazine potentiates analgesia has been around for over 40 years...despite research to the contrary.
Promethazine neither relieves pain nor potentiates opioid analgesia. In fact, one study shows that promethazine INCREASES sensitivity to pain and the amount of opioid needed to produce satisfactory pain relief.
Promethazine is very sedating and this may SEEM like pain relief because the patient may sleep more or appear calm. But a patient can be sedated without getting pain relief.