Adverse effects of diazepam include anterograde amnesia (especially at higher doses) and sedation as well as paradoxical effects such as excitement, rage or worsening of seizures in epileptics. Benzodiazepines also can cause or worsen depression. Long-term effects of benzodiazepines such as diazepam include tolerance, benzodiazepine dependence as well as a benzodiazepine withdrawal syndrome upon dose reduction; additionally after cessation of benzodiazepines cognitive deficits may persist for at least 6 months and may not fully return to normal, however it was suggested that longer than 6 months may be needed for recovery from some deficits. Diazepam also has physical dependence potential and can cause serious problems of physical dependence with long term use. However, compared to other benzodiazepines, physical withdrawal from diazepam following long term use is usually far more mild due to its long elimination half life. Nevertheless, urgent action by National Governments to improve prescribing practices has been recommended.

Advantages of diazepam are a rapid onset of action and high efficacy rates which is important for managing acute seizures, anxiety attacks and panic attacks; benzodiazepines also have a relatively low toxicity in overdose. Diazepam is a core medicine in the World Health Organization's "Essential Drugs List", which is a list of minimum medical needs for a basic health care system. Diazepam was first synthesized by Leo Sternbach, is used to treat a wide range of conditions, and has been one of the most frequently prescribed medications in the world since its launch in 1963.