Simone asked
I am taking a new medication for anxiety, lorazepam. Can you let me know how fast it works?
Answer
Ativan (lorazepam) is considered a rapid acting benzodiazepine medication, with an intermediate duration of action.
Oral Ativan Onset Of Action
Orally, Ativan is rapidly absorbed and will begin working in 15-30 minutes. However, peak concentrations in the blood occur after about two hours. Per the prescribing information for Ativan tablets:
"Ativan (lorazepam) is readily absorbed with an absolute bioavailability of 90 percent. Peak concentrations in plasma occur approximately 2 hours following administration. The peak plasma level of lorazepam from a 2 mg dose is approximately 20 ng/mL."
Parental Ativan Onset Of Action
Ativan can also be administered via intramuscular injection or intravenously and each has a different onset of action.
IM (Intramuscular injection)
When given as an IM injection, Ativan has a similar onset of action when compared to taking it by mouth, around 15-30 minutes. However, IM Ativan takes around 3 hours to reach peak concentrations in the blood, compared to 2 hours with oral Ativan. Per the prescribing information for Ativan IM injection:
"Following intramuscular administration, lorazepam is completely and rapidly absorbed reaching peak concentrations within 3 hours."
It should be noted that although it takes longer to reach peak concentrations with IM Ativan versus oral Ativan, IM Ativan reaches much higher concentrations in the blood than comparable oral doses.
IV (Intravenous)
IV Ativan has the fastest onset of action, within 15-60 seconds. Peak effects occur within 15 to 20 minutes.
IV, IM, Oral Ativan Comparison Chart
Below is a chart from the British Journal of Anaesthesia detailing blood concentrations achieved after oral, IM or IV administration of Ativan:
Source: British Journal of Anaesthesia Volume 48, Issue 10, October 1976, Pages 1017-1023
Summary
- Oral Ativan tablets have an onset of action of 15-30 minutes.
- IV Ativan has the fastest onset of action, around 15-60 seconds, while IM Ativan is comparable to oral Ativan (15-30 minutes).
- When using comparable doses of Ativan, IV Ativan will product the highest blood levels, followed by IM Ativan and then by oral Ativan.
