Patients who only briefly take opioid painkillers are still likely to face side effects, according to a new study published in the American Journal of Emergency Medicine and reviewed by Reuters Health.

While side effects associated with long-term use of the drugs have been widely studied, this is not the case with patients who take opioids for less than two weeks, said study coauthor Dr. Raoul Daoust of Hopital du Sacre-Coeur de Montreal. To learn more, Daoust and colleagues studied 386 adults who had been discharged from an emergency department with an opioid prescription, 80% of whom took at least one pill.

More than half the patients who used opioids reported feeling drowsy. Patients also reported side effects like constipation, dizziness, weakness, nausea and vomiting. Overall, 79% of patients who used the painkillers said they experienced side effects that can be related to these drugs, compared to just 38% of patients who did not use opioids.

The type of opioid being used seemed to affect patients differently. Dizziness, nausea and vomiting were more often associated with oxycodone than morphine, for example.

The side effects of opioids can severely affect patients’ quality of life, sometimes prompting them to discontinue the drugs even though they remain in pain.

Opioid-induced constipation was a particularly persistent problem in the new study. The higher the dose of opioid, the more likely patients were to feel constipated.

“It was surprising to find that 38% of patients had constipation while consuming only a (relatively low dose of opioids) during the first two weeks,” Daoust told Reuters Health in an email. Older patients were more likely to experience constipation as a side effect.

Despite the risks and the side effects, Daoust believes that opioids should not be avoided entirely. Instead, he says, patients must be properly informed of the side effects they are likely to face and given advice on how to manage them, such as avoiding driving because of possible drowsiness, or taking laxatives to manage constipation.