Drug consumption and possession exclusively for personal use have never been criminal offences in Spain. Unlike Portugal, Spain therefore had no comparable decriminalisation reform marking a before and after. This may help explain why its approach has received less international attention, both for its strengths and its problems. Unauthorised public possession or use can nevertheless attract an administrative fine. Courts assess quantity alongside other evidence when deciding whether possession was intended for personal use or supply.
The National Institute of Toxicology and Forensic Sciences (INTCF) estimates daily consumption in forensic reports. The reference to three to five days’ consumption is a criterion developed through case law to assess whether the quantity possessed is intended for personal use or supply. It is not a legally permitted allowance, and exceeding it does not automatically establish a criminal offence.
Several disputed figures concern drugs used in chemsex—using drugs to facilitate or enhance sex. In Público’s 2025 reporting, gay men in Madrid described intrusive searches, detention and trafficking charges despite maintaining that the drugs were for their own use. Madrid’s National Police denied discriminatory targeting.
Errors in established drug quantities
A paper I co-authored with lawyer Francisco Azorín Ortega examined the original reports, conducting freedom-of-information requests and appeals and making our requests publicly available allowing anyone to check the calculations made to establish decriminalised drug quantities.
For ketamine, a 2025 report takes 300 milligrams from Energy Control’s guidance for a single oral dose and treats it as a whole day’s consumption. Multiplying by five gives 1.5 grams. It does not explain this shift from one dose to an entire day, despite the relevance of repeated dosing, tolerance and route of administration.
For methamphetamine, a 2003 report assumes four daily doses of 15 milligrams, giving 60 milligrams daily and 300 milligrams for five days. A 2025 report retains that frequency without specific supporting data.
The 2025 report applies the same 0.3-gram reference to six synthetic cathinones, including mephedrone, 2-MMC and 3-MMC. Similarities in chemical structure and effects do not establish equivalent doses.
For traditional drugs such as cocaine, the report allows repeated use—up to six doses daily, yielding 7.5 grams for five days. The issue is how each reference is calculated, rather than comparing different drugs by weight alone.
The case of GHB and GBL
For gamma-butyrolactone (GBL), a 2024 report gives 12.5–62.5 millilitres for three to five days but selects 12.5, whereas other substances use the upper end. That reference is below its maximum daily estimate of 13.1 millilitres. A common 30-millilitre retail bottle already exceeds it; the INTCF itself describes routinely encountered bottles of 20–30 millilitres.
Courts also treat GBL as controlled because it converts into gamma-hydroxybutyrate (GHB), despite a 2006 order expressly excluding GHB’s esters and ethers from Spain’s psychotropic schedule. GBL is a cyclic ester of GHB.
In March 2024, the Supreme Court refused to admit an appeal, leaving a two-year prison sentence for a man carrying 30 millilitres of GBL. It endorsed inferring trafficking from quantity despite no proven transfer to another person. The bottle’s 33.9 grams were compared with 2.1 grams, an average single dose of GHB, as if covering three to five days. My recalculation, using six daily doses and the INTCF’s GHB-to-GBL conversion, gives 39.4 millilitres for five days—more than the 30 seized and over three times its 12.5-millilitre reference.
Spain’s schedules specify controlled substances and chemical forms; no general rule automatically controls unlisted analogues. Its Criminal Code prohibits extending offences beyond expressly covered cases. Prosecution based on metabolic conversion after that exclusion puts this safeguard at risk.
Flaws in these reference quantities and their application have greater consequences for people already subjected to intensive policing. Gay and bisexual men who practise chemsex have reported selective targeting; the disputed figures can provide the forensic basis for treating quantities intended for their own use as evidence of trafficking.
The calculations behind the reference quantities matter
These references originate in forensic reports, without a legislative or regulatory procedure, yet inform decisions carrying prison sentences. A 2011 seminar co-organised by the Transnational Institute and the EU’s drug monitoring agency criticised Spain’s inaccessible supporting documents.
A 2026 UN report links discriminatory drug-law enforcement to legal ambiguity, broad discretion and weak accountability.
I asked Spain’s Special Anti-Drug Prosecution Office to assess the legal basis for GBL prosecutions and the quantity criteria, coordinate corrective action and consider seeking reviews of convictions. Its 8 June 2026 decision states that its charges follow the INTCF’s 2025 report and additions, which defendants can challenge. This confirms the Institute’s practical authority in setting the quantities used to distinguish personal use from trafficking. Referring back to those same reports, while leaving their disputed calculations unanswered, illustrates the circular reasoning behind their continued use.
I approached the INTCF and the Ministry of Justice’s press office about the calculations and possible revisions. The Ministry’s communications office said its workload prevented a substantive response at present.
Lessons from other countries
International examples distinguish how quantities are calculated, what exceeding them means and how possession is punished.
In 2021, Vancouver’s drug user organisation VANDU consulted 161 members about consumption and purchasing; results suggested larger quantities than the city proposed. Pivot and VANDU argued that thresholds should protect people below them without making possession above them presumptive evidence of trafficking. Their argument distinguishes daily consumption from purchases kept for several days.
In England and Wales, Release challenged quantity categories for possession, citing tolerance and bulk buying. The Sentencing Council acknowledged that weight could produce arbitrary results; categories were based on drug class. This concerned sentencing for possession, rather than establishing intent to supply.
Mexico’s General Health Law distinguishes possession without intent to supply, including above prosecution-exempt quantities. Exceeding them does not itself establish trafficking. Instituto RIA’s 2026 guide urges assessment of circumstances rather than quantity alone.
Portugal’s 2023 reform retains quantities above ten days’ average consumption as an indication of possible non-personal use, but requires dismissal or acquittal when exclusive personal use is established. Technical rules should be reviewed, whenever possible, every six months or when scientific evidence or consumption data justify it.
UNAIDS, UNDP and INPUD’s 2026 guidance recommends indicative thresholds and additional evidence of supply, with the burden of proof remaining on the prosecution.
What Spain should do
Building on that guidance and our investigation, Spain’s health and justice authorities should commission an independent review with public sources and calculations. It should distinguish single doses, daily consumption and quantities kept for several days, and test equivalences between substances. Research should involve people who use drugs and examine purchasing patterns. Corrections must reach police, prosecutors and courts.
Harm reduction must address harms caused by drug policy. Fear of arrest can deter treatment or emergency help. The reports are public and documented errors must be corrected. A disputed consumption estimate should not substitute for evidence of intent to supply.
