Prosecuting drug impaired drivers can be difficult because of the complexities of drug toxicology. To effectively explain these complexities, as well as pertinent evidence to jurors, prosecutors must have an understanding of the basics of drug toxicology; this handbook strives to provide that understanding. Following a review of national prevalence figures on drug-impaired driving, the handbook examines the differences between alcohol and other drug-related driving while impaired (DWI) cases. DWI cases involving drugs other than alcohol are more complex for a variety of reasons, including a lack of research on some drugs and the absence of “per se” limits for drugged driving in most States beyond the per se limit on the level of ethanol allowed for vehicle operators. The prevalence rates of specific drugs in DWI cases are reviewed and include marijuana and diverted pharmaceuticals, such as pain relievers and stimulants. The drug effects for commonly abused substances are presented, including the signs and symptoms of substance use. The drug administration, absorption, distribution, metabolism, and elimination processes are also reviewed. How drugs can impair driving through the hampering of coordination, judgment and decisionmaking, perception, tracking, reaction time, and attention is described, followed by a review of how drug impairment is typically measured. The test methodology of forensic toxicology laboratories is reviewed and prosecutors are provided with advice on case preparation and how to use toxicologists as expert witnesses in DWI cases. Case studies are offered for illustration purposes. Tables, figures, endnotes, appendixes