When determining if an individual was impaired by drugs or alcohol, the court considers various factors and evidence. These may include:

1. Observations by law enforcement: The arresting officer's observations and testimony regarding your behavior, physical appearance, and performance on field sobriety tests can be influential in determining impairment. For example, if you exhibited slurred speech, bloodshot eyes, or had difficulty maintaining balance during the tests, it may suggest impairment.
2. Chemical tests: Chemical tests, such as breath, blood, or urine tests, are commonly used to measure the presence and level of drugs or alcohol in your system. These tests can provide objective evidence of impairment. For instance, a blood alcohol concentration (BAC) above the legal limit (e.g., 0.08% in many jurisdictions) can indicate alcohol impairment.
3. Expert testimony: The court may rely on expert witnesses, such as toxicologists or pharmacologists, to provide specialized knowledge and opinions on the effects of drugs or alcohol on the human body. These experts can explain how certain substances can impair cognitive and motor functions.
4. Witness testimonies: Testimonies from witnesses who observed your behavior before or during the incident can be considered. They may provide insights into your level of impairment. For instance, a witness who saw you stumbling, slurring your words, or smelling strongly of alcohol can contribute to the determination of impairment.
5. Prior convictions or records: If you have previous convictions or a history of substance abuse, the court may take this into account when assessing impairment. Repeat offenses or a documented pattern of substance abuse can strengthen the case for impairment.

It's important to note that the specific criteria and weight given to each factor may vary depending on jurisdiction and the circumstances of the case. Additionally, laws and procedures related to impairment can differ between countries and states.

References:

1. National Highway Traffic Safety Administration (NHTSA). (2018). Drug and Alcohol Testing Results: How to Interpret Them and What They Mean. Retrieved from https://www.nhtsa.gov/sites/nhtsa.dot.gov/files/809725-drug_alcohol_testing_2017_web.pdf

2. American Prosecutors Research Institute (APRI). (2010). Prosecuting Drug-Impaired Driving Cases. Retrieved from https://www.ndaa.org/pdf/prosecuting_drug_impaired_driving_cases.pdf