What do they test for in blood if blew 0.0 on breathalyzer?

First, the police are required to obtain a search warrant in order to search your blood, unless you gave them consent. If they conducted a blood test, they are looking for any substance that could impair your ability to operate a motor vehicle. Usually, they are looking for amphetamines, marijuana (THC) or a metabolite thereof, barbituates, opiates, and the like. You should consult an experienced DUI attorney for this case. You may have a number of defenses available to you. A recent change in Mississippi DUI law makes a DUI conviction a permanent part of your record for enhancement of subsequent offenses. Do not attempt to defend this on your own.

They are testing for all drugs, illegal and prescription. Benzos, marijuana, amphetamines, opiates, cocaine, etc.

If you were arrested for suspicion of driving under the influence of drugs and provided a sample of your blood, the lab will look for drugs you may have told them about as well as a general screening. If the general screening is positive in a particular category the lab will do further analysis and possibly quantify the drugs present.

You need to hire d DUI specialist.

Officer asked for blood to check for drugs in your system that may have impaired you. If you are charged, you need to consult an attorney. Based on the few facts you gave, the officer may not have had probable cause to draw blood. He needed to have reasonable articulable suspicion that you were impaired before he can draw blood. If he didn't, the evidence would be excluded and a charge of DUI or DUI metabolite would be dismissed.

They will test for a wide screen of intoxicants and mood alterants. You need an attorney.