How long will it take for a healthy adult with a blood alcohol concentration (BAC) of 0.30% to return to normal (0.00% BAC)?

Blood Alcohol Concentration Elimination Time from 0.30%

A blood alcohol concentration (BAC) of 0.30% (300 mg/dL) will take approximately 15-20 hours to return to 0.00% in a healthy adult, based on the standard elimination rate of 0.015-0.020% per hour. 1

Alcohol Elimination Kinetics

The human body metabolizes alcohol at a relatively constant rate once absorption is complete:

• Average elimination rate: 0.018% per hour (range 0.015-0.020% per hour) 1
• Individual variation exists but the rate remains fairly consistent within this narrow range for most people 1
• Elimination begins immediately after absorption starts, not after drinking stops 1

Time Calculation for 0.30% BAC

Using the standard elimination rates:

• At 0.015%/hour (slowest rate): 0.30% ÷ 0.015% = 20 hours 1
• At 0.018%/hour (average rate): 0.30% ÷ 0.018% = 16.7 hours 1
• At 0.020%/hour (fastest rate): 0.30% ÷ 0.020% = 15 hours 1

Therefore, expect 15-20 hours for complete elimination to 0.00% BAC. 1

Critical Clinical Considerations

Severe Intoxication at 0.30% BAC

• A BAC of 0.30% represents severe alcohol intoxication, nearly 4 times the legal driving limit of 0.08% 2
• This level poses significant risk for respiratory depression, loss of consciousness, and potentially life-threatening complications 2
• Medical observation is warranted during the elimination period

Withdrawal Risk Timeline

The most dangerous period begins as BAC drops, NOT during intoxication:

• 6-24 hours after last drink: Early withdrawal symptoms emerge (tachycardia, hypertension, tremors, anxiety, nausea) 3
• 48-72 hours: Highest risk period for delirium tremens (DT) in alcohol-dependent individuals 3
• 3-5 days: Peak severity of DT if it develops 3

Critical pitfall: Patients with chronic heavy alcohol use require prophylactic benzodiazepine treatment within the first 6-24 hours to prevent progression to DT, which carries up to 15% mortality if untreated 3

Factors That Do NOT Significantly Accelerate Elimination

• Coffee, cold showers, or exercise do not speed up alcohol metabolism 1
• The liver metabolizes alcohol at its fixed enzymatic rate regardless of interventions 1
• Only time eliminates alcohol from the system 1

Cognitive Function During Elimination

Do not assume cognitive capacity returns at any specific BAC threshold:

• Cognitive impairment begins at BACs as low as 0.03%, affecting visual processing and reaction times 4
• Assess cognitive function individually rather than waiting for a predetermined BAC level before psychiatric evaluation or medical decision-making 5
• Even at 0.05% BAC, significant degradation in driving performance occurs, including increased lane-keeping variability and reduced speed control 6

Monitoring Recommendations

For a patient presenting with 0.30% BAC:

• Serial clinical assessments every 2-4 hours during elimination
• Monitor for withdrawal symptoms starting at 6-12 hours 3
• Consider benzodiazepine prophylaxis if history suggests alcohol dependence 3
• Expect cognitive clearing over 15-20 hours, but assess function individually rather than by BAC alone 5