Effects of drugs on driving
CNS depressants
Like alcohol, many drugs produce CNS depression, either as a desired effect or as a side-effect of the drug. Hence much of the above discussion of alcohol applies to these types of drugs. Table 11.1 presents some common drugs with CNS depressant activity that have been implicated in impaired driving cases. Driving has been shown to be affected in driving simulators, in on-road driving studies and from epidemio logical and anecdotal reports for many drugs, including cannabis, cocaine, methamfetamine, 3,4-methylenedioxymethamfetamine (MDMA), carisoprodol, phencylidine (PCP), ketamine, opioids, benzodiazepines and gamma-hydroxy butyric acid (GHB), as recently reviewed in two special issues of Forensic Science Reviews (vol. 14, 2002, and vol. 15, 2003). Combining alcohol with prescription or recreational drugs causes an additive or synergistic effect. It is not only illegal drugs which are implicated in DUID cases. One of the most commonly encountered examples in DUID casework is that of chronic pain patients. A patient who suffers from back pain might be prescribed one or two centrally acting muscle relaxants such as carisoprodol or cyclobenzaprine, a barbiturate such as butalbital, an opioid analgesic such as propoxyphene, hydrocodone or oxycodone, a sleeping aid such as zolpidem, and often an antidepressant drug to treat the depression that typically accompanies chronic pain. The resultant combined effect makes a reduction in driving performance very likely. Whether impairment is a result of legitimate prescription use or not is immaterial from a public safety standpoint, and a driver impaired by use of prescription drugs must be subject to the same penalties as a recreational drug user.
