There aren’t any studies specifically assessing driving skills in patients taking narcotic (opioid) medications. Most of the recommendations are common-sense. Patients are told NOT to drive when there are any cognitive (mental thought processes) effects or impairments. Likewise, they should not participate in dangerous recreational or work activities.
But what are these impairments? Well, falling asleep easily would be one. Slower reflexes and reactions or decreased coordination fit this category. So does decreased concentration or clouded thought processes such as simple math calculations or making a quick decision about simple things.
Medications that are considered narcotics affect the central nervous system. The adverse effects described here are most likely to occur when the drug is first started, when increasing a dose, and when taking other drugs at the same time that can also affect the nervous system. Other drugs can refer to prescribed medications, alcohol, and illegal substances such as marijuana, cocaine, crack, meth, and so on.
In some cases, opioids can actually improve driving ability. Decreased pain (the primary intended effect of the medication) improves cognitive function. Still, anyone who is a bus driver, truck driver, pilot, or makes a living driving other types of heavy equipment should be cleared to drive by the physician prescribing the meds before before doing so on their own.