Violation of your 4th amendment rights is a defense against drug charges.
The search-and-seizure provisions of the Fourth Amendment are all about privacy. The Fourth Amendment protects against "unreasonable" searches and seizures by state or federal law enforcement authorities.
The flip side is that the Fourth Amendment does permit searches and seizures that are reasonable. In practice, this means that the police may override your privacy concerns and conduct a search of you, your home, barn, car, boat, office, personal or business documents, bank account records, trash barrel, or whatever, if:
the particular circumstances justify the search without a warrant first being issued.
When the Fourth Amendment Doesn't Protect You:
The Fourth Amendment applies to a search only if a person has a "legitimate expectation of privacy" in the place or thing searched. If not, the amendment offers no protection because there are, by definition, no privacy issues.
Courts generally use a two-part test to determine whether, at the time of the search, a defendant had a legitimate expectation of privacy in the place or things searched:
Did the person actually expect some degree of privacy?
Is the person's expectation objectively reasonable—that is, one that society is willing to recognize?