Maryland Code, Courts and Judicial Proceedings § 10-303

(a)(1) A specimen of breath or 1 specimen of blood may be taken for the purpose of a test for determining alcohol concentration.

(2) For the purpose of a test for determining alcohol concentration, the specimen of breath or blood shall be taken within 2 hours after the person accused is apprehended.

(b)(1) Only 1 specimen of blood may be taken for the purpose of a test or tests for determining the drug or controlled dangerous substance content of the person's blood.

(2) For the purpose of a test or tests for determining drug or controlled dangerous substance content of the person's blood, the specimen of blood shall be taken within 4 hours after the person accused is apprehended.