Learn More About Green Card Medical Exams & Drug Tests (jacksonwhitelaw.com)
"The standard exam does not include a drug test, but it involves urine and blood screenings that are known to catch certain drugs in your system. Generally speaking, urine tests are known to pick up “soft” drug usage within the previous two weeks, while blood tests may pick up hard drugs (though they rarely do in practice).
In addition to these standard screenings, the doctor will also ask for relevant health information, which may include drug use. If the doctor suspects that you have used illicit drugs based on your history, behavior, or physical appearance, the doctor may order a random drug screening at their discretion. The doctor can issue as little as 24 – 48 hours’ notice for a random drug screening, so they are extremely difficult to anticipate or prepare for."