Positive Urine Test for Drugs in Japan: Is the Case Already Lost? How Sampling and Forensic Analysis Are Examined

Being told that your urine tested positive is the moment many people give up. Yet a laboratory result and a proven crime are two different things. Use of stimulants is punishable under article 41-3(1)(i) of the Stimulants Control Act, and use of cannabis under article 66-2(1) of the Narcotics and Psychotropics Control Act, which came into force on 12 December 2024. In neither case does the forensic report alone settle everything. This article explains, in general terms, where room for examination usually lies.

Key points

• A urine analysis is powerful evidence, but it does not by itself establish every element of the offence.
• Where the sample was given voluntarily, the circumstances that led to it can be examined for genuine voluntariness.
• Where the sample was taken under a warrant, the issuing of that warrant and the manner of its execution may be at issue.
• The identity of the sample analysed, and how it was stored between collection and analysis, are matters to verify.
• Pinning down when and where the substance was taken is tied to intent (故意) and to the clarity of the charge.

Does a positive urine test mean there is nothing left to argue?

As a general matter, not necessarily. A forensic report states that a particular substance was detected in a particular sample. It does not automatically establish who took the substance, when, where, and with what awareness. Those are the elements that make up the offence.

None of this is to suggest that a positive result is a small thing. It is strong evidence, and no responsible lawyer would tell you otherwise. The point is narrower: if the analysis is treated as the end of the inquiry, matters that ought to be checked will never be checked, and the case will simply move forward. How much room for argument exists in any particular case cannot be judged without reading the file, so please treat what follows as a general framework rather than an assessment of your situation.

What can be questioned when police ask you to give a urine sample voluntarily?

The starting point is whether the sample really was given by your own choice. If you were kept at the scene for a long period, or placed in a situation where you could not in practice walk away, whether the submission was truly voluntary becomes a proper subject of examination.

For foreign nationals there is a further difficulty. People are asked to sign documents without fully understanding what is being requested of them. Even where an interpreter was present, whether it was made clear in your own language that the request was voluntary, and that you could decline, is a separate question. Try to recall the scene in as much detail as you can, and write down the time, the place, how many officers were present and what was said. Those notes often become the starting material for later examination.

How is a urine sample taken under a warrant examined?

Where investigators obtain a judicial warrant and take a urine sample compulsorily, the constitutional framework of the warrant requirement applies. The questions therefore become whether sufficient material was placed before the judge to justify issuing the warrant, and whether the execution stayed within the limits the warrant allowed.

In practice this is usually continuous with what happened earlier, that is, with the lawfulness of the street questioning and search of belongings that led to the warrant application. If there is a problem at the outset, that can affect how the procedures flowing from it are assessed. This has long been discussed in Japan within the framework of excluding illegally obtained evidence. For defence counsel, the work begins with requesting disclosure and painstakingly reconstructing the sequence of events.

Identity of the sample and the chain of custody

The urine collected must be the same material that was analysed, and between collection and analysis it must have been handled in a way that avoids mix-ups or degradation. These two conditions are the premise on which a forensic result can be used as evidence at all.

The matters below are typically checked. That does not mean problems are usually found. In most cases everything has been handled properly. What matters is the habit of confirming from the record that the premise holds, rather than assuming it.

• The date, time, place and witnesses to the collection, and how these were recorded
• How the container was sealed and labelled, and whether this was done in your presence
• The route and storage conditions from collection until handover to the laboratory
• How the sample is identified in the forensic report, and the analytical method used

Why do the time and place of use matter?

In use cases, the urine analysis is often the only objective evidence there is. But all it shows is that the substance was in the body during a certain window. When and where it was taken therefore usually depends on what the suspect says.

This is where the weight of a statement becomes visible. If you are unsure of your memory and go along with a date and place suggested during questioning, that account can become the backbone of the charge. Conversely, where a person may have been given the substance without knowing, or was eating and drinking with others, intent itself becomes a live question. Awareness also matters later, in the immigration process, so it is worth recording carefully at the criminal stage.

What all of this means for your status of residence (在留資格)

For foreign nationals this examination does not stop at the criminal case. Article 24, item 4, sub-item (chi) of the Immigration Control and Refugee Recognition Act (入管法24条4号チ) makes a person who has been convicted of violating the Stimulants Control Act, the Narcotics and Psychotropics Control Act and certain other listed laws subject to deportation (退去強制). It says nothing about the type of sentence or its length. A fine, or a suspended sentence, is treated the same way. A defence strategy whose final goal is a suspended sentence at trial therefore leaves the residence side of the case unfinished.

Our office builds the defence in three lines. The first is a decision not to prosecute (不起訴処分) before charges are filed. The second is contesting the deportation proceedings. The third is special permission to stay (在留特別許可). Examining the urine sampling and the forensic analysis sits at the core of the first line, and the record created there also supports the second and third. Nothing can be guaranteed, but whether the examination was done thoroughly tends to show clearly in the later stages.

Our office, and cases we have handled

At Funado International Law Office, attorney Daisuke Matsumura personally handles every stage, from the first visit at the detention facility through to the close of trial. Memories of the sampling fade quickly, so we place particular weight on hearing the details from the client at an early stage. For Chinese we have a dedicated interpreter on staff who is experienced in cases involving foreign nationals, available throughout the criminal process as an interpreter working for the client, separate from the interpreter appointed by the investigating authorities. For languages other than Chinese, we arrange an interpreter according to the needs of the case.

Past matters include a client prosecuted under the Stimulants Control Act for possession with profit-making purpose (営利目的), where thorough analysis of the evidence, examination of the defendant and cross-examination led to an acquittal. In another matter, a client accused of acting as a collector in an organised fraud scheme was rearrested several times; through careful handling of the interrogations and repeated objections, decisions not to prosecute were obtained on every count.

When a forensic result is put in front of you, what happens next depends on whether you stop thinking there or go back and test the premises. Read the record, verify what should be verified, and only then choose a course. In our experience that sequence is the surest one. Please note that this article is a general explanation; for your own case, consult a lawyer directly. Past results reflect the particular circumstances of those cases and are not a guarantee of a similar outcome.

This article reflects the law as at August 2026.

About the author

Daisuke Matsumura, Attorney at Law
Dai-Ichi Tokyo Bar Association (registration no. 59077, admitted 2019)
Funado International Law Office (Fuse Building Main Wing 3F, 3-4-10 Takada, Toshima-ku, Tokyo)
Practice focused on criminal defence for foreign nationals and immigration proceedings.
Results include an acquittal in a Stimulants Control Act case (possession for the purpose of profit), non-prosecution in organised fraud cases, and special permission to stay in cases regarded as difficult.

Funado International Law Office
Website: https://matsumura-lawoffice.jp/
WeChat ID: matsumura1119