How long does alprazolam (Xanax) last?

Duration of Action for Alprazolam (Xanax)

Alprazolam typically lasts 11-16 hours based on its elimination half-life, with peak effects occurring 1-2 hours after oral administration and clinical effects generally persisting for 4-6 hours before requiring redosing. 1

Pharmacokinetic Profile

The FDA-approved labeling provides the most authoritative data on alprazolam's duration:

• Elimination half-life: 11.2 hours (range: 6.3-26.9 hours) in healthy adults 1
• Peak plasma concentration: Occurs 1-2 hours after oral administration 1
• Peak levels: 8.0-37 ng/mL over the 0.5-3.0 mg dose range 1
• Bioavailability: 80-100% when taken orally 2

The half-life determines how long the drug remains in your system—after approximately 11 hours, half of the dose has been eliminated. However, the clinical duration of noticeable effects is typically shorter than the elimination half-life, usually requiring dosing 3-4 times daily for sustained anxiety control 3, 4.

Extended-Release Formulation

For patients requiring longer duration:

• Alprazolam XR (extended-release) is designed to deliver therapeutic concentrations for 24 hours after once-daily dosing 5
• This formulation avoids the sudden peak concentrations of immediate-release alprazolam, reducing abuse potential and side effects like sedation 5
• The extended-release version eliminates breakthrough anxiety between doses that commonly occurs with immediate-release formulations 5

Factors That Modify Duration

Several patient-specific factors significantly alter how long alprazolam lasts:

Age and Organ Function

• Elderly patients: Mean half-life increases to 16.3 hours (range: 9.0-26.9 hours) compared to 11.0 hours in younger adults 1
• Alcoholic liver disease: Half-life ranges from 5.8-65.3 hours (mean: 19.7 hours), nearly doubling the duration 1
• Obesity: Half-life increases to mean of 21.8 hours (range: 9.9-40.4 hours) 1

Race and Smoking

• Asian patients: Experience approximately 25% longer half-life compared to Caucasians 1
• Cigarette smokers: May have up to 50% reduction in alprazolam concentrations, effectively shortening duration 1

Drug Interactions Affecting Duration

Critical interactions that prolong alprazolam's effects by inhibiting CYP3A4 metabolism:

• Ketoconazole: Increases exposure 3.98-fold 1
• Itraconazole: Increases exposure 2.70-fold 1
• Nefazodone: Increases exposure 1.98-fold 1, 6
• Fluvoxamine: Increases exposure 1.96-fold 1, 6
• Cimetidine and oral contraceptives: Reduce clearance and increase half-life 7

When nefazodone is coadministered, alprazolam dose must be reduced by 50% to avoid excessive sedation and prolonged effects 6.

Conversely, carbamazepine (a CYP3A4 inducer) shortens the half-life from 17.1 hours to 7.7 hours, requiring dose adjustments 1.

Clinical Implications

Common pitfall: Patients and providers often confuse the elimination half-life with the duration of therapeutic effect. While alprazolam remains detectable in the body for 11+ hours, the anxiolytic effects typically wane after 4-6 hours, necessitating multiple daily doses with immediate-release formulations 3, 4.

For sustained anxiety control throughout the day, either:

• Dose immediate-release alprazolam 3-4 times daily 3
• Use alprazolam XR once daily for 24-hour coverage 5

Withdrawal risk: The relatively short half-life compared to longer-acting benzodiazepines like clonazepam (30-40 hours) 8 means alprazolam carries higher risk of interdose withdrawal symptoms and rebound anxiety, particularly problematic when doses are missed 5.