Q: Is it against the law to have used an illegal controlled substance in the past?

A: In general, past use of an illegal drug is unlikely to lead to legal proceedings. It is legally the same as having committed any other minor criminal act: The more recent the use, the more evidence there is for the act, the more problematic it becomes.

The following should not be taken as legal advice. If you need legal help, please seek the advice of a lawyer.

People primarily ask about the legal risks of past use because they want to be able to talk or write about their experiences. When describing past illegal acts, mentioning specifics about timing and location increases risk of prosecution. If the statute of limitations has not run out, it is possible that a judge could grant a search warrant--or in extreme cases, an arrest warrant--based on specific details of past use. In some areas, a positive drug test is treated as evidence of a crime.

The statute of limitations on controlled substance violations differs dramatically from one jurisdiction to another. In many areas prosecution is limited to five (or seven) years after the crime is committed. Others start the clock counting only when police have evidence of the crime in hand. And in a small but growing number of locations, there is no statutory limit on prosecution of drug offenses.

Violations that have happened within the statute-limited period can be prosecuted if there is enough evidence. Simply talking about past use, by itself, is very unlikely to be considered proof of a crime, which means the authorities would need to have additional evidence to prove their case (or even get an arrest warrant). It is important to note, however, that out-of-court documented admissions of law violations can be strong evidence if a trial does take place.

In most states, "possession" of a controlled substance is illegal but "use" of the substance is not. Because of this, in these jurisdictions, there would need to be evidence of past possession before charges could be brought. This evidence could exist in the form of photographs, video, or the testimony of others, but even these might not lead to prosecution if the quantities were small and sales were not involved. As long as the individual is no longer in possession of illegal materials, past possession of small quantities of an illegal substance is unlikely to ever be prosecuted.

In some places, local or state laws have been passed making use of a controlled substance illegal. This can take the form of specific legislation against "ingestion" or "use" (usually as a misdemeanor) or by redefining the term "possession" to include the presence of a controlled substance in the body after it has been ingested. In at least one jurisdiction, a positive drug test can be grounds for prosecution.

A recent case in South Dakota (S. Dakota v. Schroeder) has received some press because a man who tested positive for amphetamines was prosecuted for "possession" of an illegal substance based solely on a positive drug test.1 A man was pulled over by police who searched his car. After the police found a scale under the driver's seat the defendant consented to a urine test, which came back positive for methamphetamine. Based on this evidence alone, the defendant was convicted of possession of a controlled substance.2

He and his lawyers argued that he should be charged under South Dakota's "ingestion" laws which make it a misdemeanor to take a substance into the body for the purpose of intoxication (with the exceptions of alcohol and prescribed medications).

"Any person who intentionally ingests, inhales, or otherwise takes into the body any substance, except alcoholic beverages [...] for purposes of becoming intoxicated, unless such substance is prescribed by a practitioner of the medical arts [...], is guilty of a Class 1 misdemeanor."3

Instead, he was prosecuted under the felony "possession" laws. The case made its way to the South Dakota Supreme Court in February 2004 where his conviction was upheld. That court decided that a recent change to the wording of the state's controlled substance laws made it clear that the legislature intended a positive drug test to be prosecutable under the "possession" laws. The new wording includes in the definition of a controlled substance: "an altered state of a drug or substance listed in Schedules I through IV absorbed into the human body."2

With this rewording South Dakota has made the presence of both controlled substances and metabolites of controlled substances in the human body the equivalent of possession of a controlled substance. The only evidence needed is a positive drug test.

The Schroeder case, though unusual, is an example where recent past use was prosecuted as a crime. It is now possible for drug tests conducted on hair to detect use of some controlled substances from more than 3 months prior; with the improvement in drug testing techniques, this period will continue to lengthen. In jurisdictions with laws similar to South Dakota, it is possible that a positive drug test from three or four years ago could be used as the primary evidence for charges of either illegal use or illegal possession as long as the statute of limitations has not expired.

Suggestion or evidence of past illegal substance use could pose a problem even if there is not enough evidence to support criminal charges. A few scenarios where this could be an issue are: in a fight for custody of children, if a parent's past use is brought to the attention of child protective services, and in the workplace, where the mere suggestion of drug use could lead to the loss of one's job or professional license.