On July 1, 1999, Sweden implemented zero-concentration limits for controlled drugs in drivers. Eliminating the need to prove that a person's ability to drive safely was impaired by drugs has greatly simplified prosecution, which now rests primarily on the forensic toxicology report. A large case series of driving under the influence of drugs (DUID) suspects was compared before and after introducing zero concentration limits for controlled substances.

Immediately after the zero-limit law came into force, the number of cases of DUID submitted by the police for toxicological analysis increased sharply and is currently ten-fold higher than before the new legislation. Statistics show that about 85% of all blood samples sent for toxicological analysis have one or more banned substances present.

Amphetamine is by far the leading drug of abuse in Sweden and was identified in about 50-60% of all DUID suspects either alone or together with other controlled substances. The next most frequently encountered illicit drug was tetrahydrocannabinol (THC), with positive findings in about 20-25% of cases.

Various prescription drugs, mainly sedative-hypnotics, were also highly prevalent and these occurred mostly together with illicit substances. Opiates were high on the list of substances identified.

Most DUID suspects in Sweden were men (85%) who were poly-drug users combining illicit substances, like amphetamine and/or cannabis, with a prescription medication such as various benzodiazepines.

Sweden's zero-concentration limit has done nothing to reduce DUID or deter the typical offender because recidivism is high in this population of individuals (40-50%). Indeed, many traffic delinquents in Sweden are criminal elements in society with previous convictions for drunk and/or drugged driving as well as other offenses.

The spectrum of drugs identified in blood samples from DUID suspects has not changed much since the zero-limit law was introduced. The study was conducted by A.W. Jones and appeared in Traffic Injury Prevention, Vol. 6, No. 4, 2005.

Reprinted from the Winter 2006 issue of the Reporter, the newsletter of the International Council on Alcohol, Drugs and Traffic Safety.