When you drive or attempt to drive a vehicle, boat, or OHRV (Off Highway Recreational Vehicle),on any public highway or waterway, you are giving the state permission, or “consenting” to drug or alcohol tests if the police have reasonable grounds to believe you are under the influence. You are agreeing to physical tests and examinations, and to chemical, infrared molecular absorption, gas chromatograph test, and blood, urine or breath tests.

These tests are administered by the police either on the side of the road, at the police station or in a lab. The results of field sobriety tests, such as walking a straight line and touching your nose, and the breath test are given to you as soon as the test is completed. The results of lab tests are sent to you within 48 hours of receipt. (Make sure the Department of Motor Vehicles has your correct address on file, or you may not receive all the paperwork that is relevant to your case.) In New Hampshire, you will be considered as Driving While Intoxicated if you have a blood alcohol content (BAC) of 0.08 or more, 0.02 if you are under the age of 21, and 0.04 if you are driving a commercial vehicle.

Before administering a test, the police officer must follow certain prerequisites. Statute 265-A:8 defines the prerequisites as:

I. Before any test of a person's blood, urine, or breath specified in RSA 265-A:4 is given, the law enforcement officer, authorized agent, or peace officer shall:
(a) Inform the arrested person of his or her right to have a similar test or tests made by a person of his or her own choosing;

(b) Afford the arrested person an opportunity to request such additional test; and

(c) Inform the arrested person of the consequences of his or her refusal to permit a test at the direction of the law enforcement officer.

II. Before any post-arrest physical test specified in RSA 265-A:4 is given, the law enforcement officer, authorized agent, or peace officer shall inform the defendant of the consequences of the defendant's refusal to comply with the law enforcement officer's, authorized agent's, or peace officer's instructions for a post-arrest physical test.

In New Hampshire, as in many states, if you refuse to perform a test and you are found guilty of DWI, you will automatically lose your license for a set period. This is known as Administrative License Suspension. In New Hampshire a suspension of six months is imposed if you have no previous DWI's or test refusals. If you have had a prior DWI conviction or test refusal, the state will suspend your license for two years.

If the prerequisites are not followed, the tests cannot be used against you in court.