Whatever the cause of the impairment, from the standpoint of public safety an impaired driver is dangerous to other people and to property. Although drunk driving laws have long been in effect and are relatively clear and consistent, the process of developing similar standards for driving while under the influence of drugs or medications, or a combination of drugs and alcohol, has proved to be more difficult. Historically, many states have attempted to compensate for the difficulty in proving a drugged driving case by imposing more serious consequences for that offense than for driving while intoxicated from the use of alcohol.
With the recent increase in the number of prescriptions for potentially intoxicating drugs and the significant rise in rates of abuse of medications as recreational drugs, as well as medical marijuana laws and decriminalization of marijuana in a number of states, states have attempted to pass new laws that are more effective at deterring and punishing driving that is impaired by drug use.
The automobile age coincides with an increased number of laws that prohibit certain recreational drugs, as well as with the passage and repeal of prohibition, and the impaired driving laws of earlier eras reflect that history. Intoxication by alcohol was recognized as causing significant impairment of a person's ability to drive. Drugged driving laws were drafted with illicit drugs in mind, without the presumption that specific blood levels of drugs or drug metabolites were evidence of intoxication. Due to the relative infrequency of drug testing, drugged driving charges seemed most likely to be brought following an accident in which the driver was injured, based upon blood or urine screening administered by a hospital.
In more recent years, some legislatures have passed laws that attempt to create the equivalent of a "per se" drunk driving charge, a legal limit for blood alcohol over which a driver is presumed to be intoxicated, by setting similar thresholds for certain drugs or metabolites associated with drug use. That process has been complicated by the difficulty of establishing meaningful standards, given issues such as drug tolerance or the lack of correlation between the defined forbidden blood levels and actual intoxication, as well as by the rise of prescription drug abuse and marijuana decriminalization. Nonetheless, approximately one third of U.S. states have passed "zero tolerance" laws that criminalize driving with any amount of a prohibited substance present in a driver's blood, urine or saliva. Some states have significantly increased the blood testing for cases of suspected impaired driving, and in some jurisdictions police officers are trained to take blood samples from suspects for analysis.
Abuse of Prescription Medication
Although the abuse of pharmaceuticals is far from new, since the introduction of modern anti-anxiety medications, prescription sleep aids, and powerful prescription pain medications, the number of people who use prescription drugs as recreational drugs has dramatically increased. This trend has increased the need for more effective laws against operating under the influence of drugs, but it can be difficult to legislate against driving following the the recreational use of prescription drugs without potentially making it a criminal act to drive a car after taking a prescription as ordered by a doctor.
With almost half of the states having passed medical marijuana laws, and a few decriminalizing marijuana use by adults, legislatures have turned their attention to how legal marijuana use affects driver safety. Some states have introduced "zero tolerance" laws that prohibit operating a motor vehicle when a driver tests positive for any amount of marijuana usage, even though that use may have occurred days, weeks, or in some cases a month or more before the traffic incident.
No driver is permitted to operate a vehicle while impaired by drugs or alcohol. Even if a driver takes only prescription medications, and takes them exactly as prescribed, if the person's ability to safely operate a motor vehicle is impaired by those medications the person may be charged with operating under the influence of drugs. Identifying the consumption of drugs as the cause of impaired driving becomes more difficult when the driver is also fatigued, or where a legislature attempts to set a per se limit or zero tolerance standard that could result in conviction even in the absence of impairment.
Arbitrary Per Se Standards for Operating Under the Influence of Drugs
Even in the context of alcohol, per se limits can at times be arbitrary. Although most people respond to alcohol in a predictable manner, and people with lower alcohol tolerance can be prosecuted under impaired driving laws even if below the legal limit, some people have high tolerance for alcohol and show little to no sign of impairment at blood alcohol levels at which most people would be very obviously impaired, even incapacitated.
As a society, we have determined that it is better to set a blood alcohol limit that is accurate for most drivers, while expecting those whose tolerance levels are unusually high to nonetheless refrain from drinking excessively before driving a vehicle. Although in a sense the laws are unfair to that population of heavy drinkers, they know how much alcohol they have consumed and their blood alcohol levels will usually be below the legal limit within a few hours of when they stop drinking, so the burden on them is relatively slight as compared to the benefit to society from keeping impaired drivers off of the road. Zero tolerance laws for operating a vehicle after alcohol consumption apply to minors, who are already legally prohibited from drinking. While blood, breath, and urine test results may potentially give different results, the results remain highly reflective of actual alcohol consumption, and a suspected drunk driver is normally able to request a second test modality (such as a blood or urine test, following a positive breath test) to verify the results of the initial test.
Drug and pharmaceutical use is more complicated. As with alcohol, many drugs and medications create tolerance in the user, and usage or prescription levels will increase over time to maintain the same effect. For somebody who receives a prescription opiate or opioid medication, such as Vicodin or Oxycontin, over time a blood level that would suggest intoxication for an average person, and once was likely intoxicating even to the patient, may be well below the levels that would be intoxicating to the patient. The same is true of anti-anxiety medications, including benzodiazepines such as Xanax and Valium.
Testing for Levels of Drugs and Pharmaceuticals
Testing for drugs may be based upon testing for the parent drug (the actual drug or medication consumed by the allegedly intoxicated person) but far more often is based upon levels of metabolites in the suspect's blood or urine. Metabolites are the chemicals formed by the body as it processes the drug, as opposed to directly measuring the level of the medication in a person's body. For some drugs and medications, metabolites will be present for days or weeks after use, and metabolite levels are often a very poor indication of when the drug was consumed or when any intoxicating effect wore off. Also, metabolite levels can be considerably different between blood, urine and saliva tests, even when samples are taken from the same person at the same time. Metabolites themselves rarely have any psychoactive element, meaning that metabolite levels are often poor evidence of intoxication.
While as a society we might take a similar attitude toward illicit drug use to that behind zero tolerance alcohol laws directed at minors -- as any use at all is illegal, any appreciable blood level should support a criminal charge without respect to whether the level suggests any impairment -- one significant difference remains: While alcohol passes out of the body in a relatively rapid and predictable manner, many pharmaceuticals do not. Testing for metabolite levels can be an accurate gauge of whether a driver has used a specific medication or controlled substance in the past, but may be a very poor indication of when the consumption occurred, when any intoxicating effect wore off, or even if the person who took a medication was intoxicated at all from its consumption.
As with any impaired driving charge, convictions for driving under the influence of drugs carry consequences that include possible incarceration, driver's license suspension or revocation, fines and court assessments, screening for substance abuse, attendance in a substance abuse support group, and community service or participation in a work program. In most jurisdictions, the penalties for drugged driving are greater than the penalties for driving under the influence of alcohol. In a few jurisdictions, even a first offense conviction of drugged driving can be a felony, carrying a possible prison term.
Where a driver is charged with the offense of driving while visibly impaired, the most common defenses are the same as in any impaired driving case:
Lack of Probable Cause - The traffic stop was not supported by probable cause.
Lack of Impairment - The conduct alleged to constitute impairment was ordinary driving conduct, or was the result of something other than intoxication, such as fatigue.
Contradictory Evidence - Photographic or video evidence, such as footage from the officer's patrol vehicle dash camera, or witnesses weaken or contradict the officer's statements about the driver's alleged impairment.
When the charge is based on an unlawful blood alcohol level, the defense of impaired driving charges becomes more complicated. While some of the defenses are the same as an alcohol impairment case, drugged driving laws potentially implicate additional defenses, depending on the state's statutory law and case law, as well as constitutional issues:
Chemical Test Rights - Was the impaired driving suspect informed by the officer of his or her chemical test rights before the test was administered.
Test Administration - Was the blood or urine sample being used to support the charge properly taken and properly analyzed.
Chain of Custody - Was the sample properly handled after it was taken to avoid potential contamination, spoilage, or confusion with samples from other cases.
Toxicology - Is the state's allegation of impairment properly supported by medical science.
Due Process - Does a per se standard that criminalizes sober driving based upon an act that occurred a significant time before the traffic stop, perhaps days or weeks before, and which may be completely legal, violate the driver's constitutional rights.
While it can be difficult to balance road safety with the fact that millions of people take prescription drugs that have the potential to cause unsafe driving, it is not reasonable to criminalize sober driving by a person who has not broken any laws, and who has not demonstrated an impaired ability to drive, based upon the fact that their blood contains traces of a prescription medication that they are taking in accord with their doctor's instructions. At the same time, doctors should emphasize to patients when a prescription may affect their driving ability, and patients should pay attention to warnings given by their doctor or pharmacist, and the labels on their prescription bottles about not driving or operating heavy equipment after taking a potentially intoxicating medication.
The defense to a drugged driving charge may quickly become very technical and complex. Given the significant stakes involved, with significant fines, driver's license sanctions and possible incarceration, and in some states the potential of a felony record for even a first offense, it makes sense for any person charged with driving while under the influence of drugs to work with a criminal defense lawyer who is experienced in the defense of drugged driving cases.