Xanax (alprazolam) is a medication used to treat anxiety and panic disorders. One dose of Xanax can last anywhere from 31 hours to 134.5 hours (5.6 days) in the body, depending on factors related to the individual who took it. However, the calming, relaxing, and sedative effects of Xanax usually wear off within about eight to twelve hours.

Xanax is taken by mouth and quickly absorbed into the bloodstream. Effects should be noticed within an hour and the medicine reaches peak concentrations in the body after one to two hours. People who take Xanax regularly can build up a tolerance to it and effects, such as a feeling of calm or sedation, may take longer to develop or not be felt as strongly as before.

Xanax is usually prescribed three times a day because its effects in the body (calming, sedation, relaxing) tend to wear off within eight hours for most people. However, one dose of Xanax remains detectable in the body for two to five days – the exact length of time depends on several factors specific to the individual who took the dose.

What factors determine the half-life of Xanax?

Factors that determine how long a dose of Xanax will persist in the body for include:

• A person’s age: Xanax lasts for longer in elderly people. The average half-life in the elderly is 16.3 hours, compared to 11.2 hours in younger, healthy adults
• Weight: Xanax lasts for longer in heavier people, because obesity makes it harder for your body to break down Xanax. The average half-life in people who are overweight/obese is 21.8 hours, compared to 11.2 hours in young, healthy adults
• Ethnicity: Xanax lasts for longer in Asian people. The average half-life in Asian people is 14 hours, compared to 11.2 hours in Caucasians
• Metabolism: People who exercise a lot or who have a faster metabolism clear Xanax faster than those who don’t exercise or do any physical activity. The half-life of Xanax is shorter in these people
• Liver function: Xanax lasts for longer in people with poor liver function. The average half-life in people with alcoholic liver disease is 19.7 hours, compared to 11.2 hours in young, healthy adults
• Length of time taking Xanax: If you take Xanax regularly, then you will have a higher concentration in your bloodstream and it will take longer to fully eliminate it all. But because you have built up a tolerance to the drug, you may not necessarily feel its effects for longer
• Interacting medications: Xanax lasts longer when it is taken with drugs that inhibit CYP3A4 (eg, erythromycin, ketoconazole, nefazodone, oral contraceptives), one of its metabolizing pathways. Other drugs (such as carbamazepine, St John’s wort), may decrease the half-life of Xanax
• Smoking: The half-life of Xanax may be reduced by up to 50% in smokers compared to nonsmokers. This means that smokers metabolize Xanax more quickly than nonsmokers
• Alcohol: Alcohol can increase the effects and half-life of Xanax, and can lead to dangerous side effects which could be fatal.

How long does Xanax stay in your system?

Studies have shown that the half-life of Xanax ranges from 6.3 to 26.9 hours. It is important to realize that half-life is a figure that is an estimate of the time it takes for the concentration or amount in the body of that drug to be reduced by exactly one half (50%). After four to five half-lives, 97% of a drug has cleared from the body, and the drug is no longer considered to be having any effect. However, this does not mean that it won’t be detectable by a drug test, as this depends on how specific and sensitive the drug test is.

If we use the average half-life of Xanax, which is 11.2 hours, then the following is estimated for a 1mg dose of Xanax:

• 11.2 hours after administration, 0.5mg remains
• 22.4 hours minutes after administration, 0.25mg remains
• 33.6 hours after administration, 0.125mg remains
• 44.8 hours after administration, 0.063mg remains
• 56 hours after administration, 0.0315mg remains.

In theory, we can see that after 56 hours (2.3 days), almost all the original Xanax dose (slightly less than 97%) has been eliminated in people whose Xanax half life is 11.2 hours. However, in some people, the half-life of Xanax is 26.9 hours. In these people, it will take approximately 134.5 hours (5.6 days) for almost 97% of a dose of Xanax to be eliminated.