From the FDA Drug Label
Peak concentrations in plasma occur approximately 2 hours following administration The time it takes for lorazepam (Ativan) to take effect is not directly stated in terms of onset of action, but peak concentrations are reached in approximately 2 hours.
- The onset of action may be sooner, but the exact time is not specified. 1
From the Research
Lorazepam typically begins to take effect within 15-30 minutes when taken orally, with peak effects occurring around 1-2 hours after administration, as supported by the most recent study on the pharmacokinetics of extended-release lorazepam 2. The onset of action can be faster (within 5-10 minutes) when administered intravenously in medical settings. Individual factors such as metabolism, body weight, age, and whether the medication is taken with or without food can influence how quickly you feel the effects. The initial calming effects may be noticeable shortly after taking the medication, while the full therapeutic effects for anxiety or insomnia may take a bit longer to develop. Some key points to consider when taking lorazepam include:
- The medication works by enhancing the effects of gamma-aminobutyric acid (GABA), a natural chemical in the brain that inhibits brain activity, which helps reduce anxiety, relax muscles, and induce sleepiness.
- If you're taking lorazepam as prescribed and don't feel any effects within an hour, it's essential not to take additional doses without consulting your healthcare provider, as this medication can cause dependence and has potential for overdose when taken incorrectly, as highlighted in studies on the risks of benzodiazepines 3, 4.
- The most recent study on the pharmacokinetics of extended-release lorazepam 2 provides the most up-to-date information on the medication's effects and is therefore the primary basis for this recommendation. It's also important to note that lorazepam can cause rebound insomnia and withdrawal phenomena, as seen in a study on the effects of lorazepam on sleep and withdrawal 5. However, the most recent and highest-quality study 2 takes precedence in guiding clinical decision-making.