A single 5mg dose of diazepam typically produces noticeable effects for about 4 to 6 hours, though the drug remains active in your body far longer than that. The calming, muscle-relaxing peak hits within 1 to 1.5 hours of swallowing a tablet, then gradually tapers. But diazepam is a long-acting benzodiazepine, and its full story plays out over days, not hours.
How Long You’ll Feel the Effects
Diazepam is absorbed quickly from the gut, reaching peak blood levels roughly 30 to 90 minutes after an oral dose. At 5mg, most people notice reduced anxiety, mild sedation, and muscle relaxation during this window. These primary effects fade over the next several hours as the drug redistributes from the brain into fat tissue throughout the body.
By about 4 to 6 hours, the strongest effects have worn off. But subtler effects like mild drowsiness, slightly slower reaction times, and residual relaxation can linger well beyond that. Many people report feeling “off” or slightly foggy the next morning, especially if they took the dose in the evening. This isn’t unusual and reflects the drug’s unusually long elimination timeline.
Why Diazepam Stays in Your Body So Long
Diazepam has a half-life of 21 to 37 hours, meaning it takes that long just to clear half the dose from your bloodstream. But the real issue is what your liver turns it into. As your body breaks down diazepam, it produces an active metabolite called nordiazepam, which has its own half-life of 31 to 97 hours. Nordiazepam still acts on the same brain receptors as diazepam itself, so even after the parent drug fades, its byproduct continues working at a low level.
This chain of active metabolites is what makes diazepam fundamentally different from shorter-acting alternatives. A single 5mg dose can take 5 to 8 days to fully clear your system when you account for all active breakdown products. If you take multiple doses over several days, blood levels build up and need 5 to 14 days of consistent dosing to reach a stable plateau.
Factors That Extend the Duration
Your age is the single biggest variable. In older adults, diazepam and its metabolites can have half-lives stretching to 96 hours. The liver enzymes responsible for clearing the drug slow down with age, reducing clearance by roughly 30 to 40 percent. A 5mg dose that wears off by evening in a 25-year-old may produce noticeable next-day grogginess in a 70-year-old.
Liver health matters just as much. Since diazepam depends heavily on liver processing, any condition that impairs liver function (hepatitis, cirrhosis, fatty liver disease) can significantly extend how long the drug and its metabolites circulate. Body composition plays a role too. Diazepam is highly fat-soluble, so it accumulates in fatty tissue and releases slowly back into the bloodstream. People with higher body fat percentages may experience a longer tail of low-level effects.
Certain medications also slow diazepam’s breakdown. Drugs that interfere with the same liver enzymes, including some calcium channel blockers, antifungal medications, and stomach acid reducers, can meaningfully increase the amount of diazepam your body is exposed to and extend its half-life. One study found that diltiazem, a common heart medication, significantly increased diazepam levels and prolonged its elimination regardless of a person’s genetic makeup for processing the drug.
How Long It Shows on a Drug Test
Standard urine drug screens can detect diazepam and its metabolites for up to 10 days after a single dose. This long detection window exists because the test picks up not just diazepam itself but also nordiazepam, oxazepam, and temazepam, all of which your body produces as it breaks diazepam down. The actual window depends on the dose, how often you’ve taken it, and your individual metabolism, but 10 days is the upper estimate for long-acting benzodiazepines in lab testing guidelines from Mayo Clinic Laboratories.
If you’ve been taking diazepam regularly, expect a longer detection window. Repeated doses allow the drug and its metabolites to accumulate in tissue, and it takes considerably longer for everything to wash out once you stop.
The Difference Between “Wearing Off” and “Gone”
This distinction trips people up. When the anxiety relief or sedation from a 5mg dose fades after 4 to 6 hours, the drug is not gone. It’s still circulating, still mildly active, and still affecting your coordination and judgment at levels you may not consciously notice. This matters for driving, operating machinery, and drinking alcohol. The residual drug in your system amplifies the effects of alcohol and other sedatives even a full day later.
It also matters for dosing. Because diazepam and its metabolites stick around so long, taking another dose before the first has cleared means you’re stacking. Each subsequent dose adds to whatever is still in your system from the last one, which is why side effects like excessive drowsiness and poor coordination tend to build over the first week or two of regular use before leveling off.