Opioid analgesics commonly cause drowsiness, dizziness, and respiratory depression. However, these side effects usually disappear with continued use. However, constipation, another common side effect, tends to persist. In addition, opioid use may lead to addiction or dependence. Other possible side effects of opioid analgesics include:
- Euphoria, dysphoria, agitation, seizures, hallucinations
- Lowered blood pressure and heart rate
- Muscular rigidity and contractions
- Nausea and vomiting
- Non-allergic itching
- Pupil constriction
- Sexual dysfunction
- Urinary retention
The benchmark drug in this class is morphine — with other opioids falling above or below it in terms of pain-relieving potential. Near the bottom of the list is codeine, usually prescribed in combination with acetaminophen to relieve, for example, pain resulting from dental work. Codeine is only about 1/10th as powerful as morphine.
Opioids more powerful than morphine include hydromorphone (Dilaudid) and oxymorphone (Opana). But the strongest opioid in community use is fentanyl which, in its intravenous form, is 70 to 100 times more potent than morphine.
Fentanyl is also available as a long-release patch (Duragesic) and as a lozenge that dissolves in the mouth (Actiq). Sufentanil is even more powerful than fentanyl, but its use, at present is restricted to the intravenous route. However, a transdermal patch containing sufentanil is in clinical trials.