Diazepam (Valium) is a long-acting benzodiazepine that typically reaches its peak concentration in the blood within 30 to 90 minutes after oral ingestion. When used for sleep onset or as a sedative, most people begin to feel a noticeable "calming" or drowsy effect within 15 to 60 minutes. It is important to note that while it can help one fall asleep quickly due to its muscle-relaxant and anti-anxiety properties, diazepam is not always the first choice for chronic insomnia because of its very long "half-life" (ranging from 20 to 100 hours). This means the drug stays in the system for a long time, which can lead to significant daytime grogginess or a "hangover effect" the next morning. In 2026, medical professionals typically advise taking it roughly 30 to 60 minutes before your intended bedtime. Always consult a doctor before use, as it carries a high risk of dependence and can interact dangerously with other substances like alcohol, which significantly amplifies its sedative effects.