Final answer:
A BAC test is the most accurate method to determine intoxication levels, considering the liver metabolizes alcohol at a fixed rate and several biological factors can influence sobering up.
Step-by-step explanation:
The most accurate way to determine a person's level of intoxication is through a Blood alcohol concentration (BAC) test. Blood or breath testing can be used to measure the BAC, which legally defines intoxication at various levels, typically above 0.08% in the United States. While breathalyzer tests provide a good estimate of BAC by measuring the ethanol concentration in a person's breath, blood tests are more definitive.
It's important to understand that factors such as age, sex, body composition, and general health can affect how quickly alcohol is metabolized, and thus how it affects an individual's BAC. The liver breaks down alcohol at a steady rate, and no amount of coffee or cold showers can speed up this process, so giving the body time is the only way to reduce intoxication.