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5F-ADB

5F-ADB, also designated as 5F-MDMB-PINACA, is a synthetic cannabinoid receptor agonist belonging to the indazole-3-carboxamide class, characterized by the molecular formula C_{20}H_{28}FN_{3}O_{3} and featuring a fluorinated pentyl chain attached to an indazole core. It functions primarily as a high-affinity agonist at the cannabinoid CB1 receptor, demonstrating an EC_{50} value of approximately 0.59 nM, rendering it roughly 290 times more potent than Δ^{9}-tetrahydrocannabinol (THC). Emerging on the designer drug market around 2014, 5F-ADB has been clandestinely manufactured and distributed in products marketed as legal alternatives to , such as herbal blends laced with the compound to evade detection in standard drug tests. Lacking any established therapeutic or medical applications, its recreational use produces cannabimimetic effects including and relaxation, but at doses it elicits severe adverse reactions due to its exceptional potency and the persistence of active metabolites that retain CB1 . 5F-ADB's toxicity profile is marked by associations with acute intoxications and fatalities, including approximately ten deaths in linked to its consumption, often involving or cardiac events, with concentrations as low as 1.17–7.95 ng/g. Symptoms reported in non-fatal cases encompass , seizures, , , and respiratory , underscoring its disproportionate risk relative to natural cannabinoids. In response to concerns, it was temporarily scheduled and subsequently placed permanently in Schedule I of the United States in 2019, reflecting its high abuse potential and absence of accepted safety for use under medical supervision.

Chemical Properties

Structure and Synthesis

5F-ADB, chemically known as 5F-MDMB-PINACA, features a central 1H-indazole ring system substituted at the N-1 position with a 5-fluoropentyl chain (-CH₂CH₂CH₂CH₂CH₂F) and at the C-3 position with a (-C(O)NH-) linked to a (2S)-1-(methoxycarbonyl)-2,2-dimethylpropyl moiety, equivalent to a modified tert-leucine methyl . This configuration classifies it as an indazole-3-, with the full systematic name methyl (2S)-2-[[1-(5-fluoropentyl)-1H-indazole-3-carbonyl]amino]-3,3-dimethylbutanoate. The fluorination at the terminal position of the pentyl chain introduces and metabolic stability compared to non-fluorinated analogs. Unlike Δ⁹-tetrahydrocannabinol (THC), which has a fused dibenzopyran core, 5F-ADB's scaffold mimics pharmacophoric elements for interaction through the hydrogen-bond donor and the extended alkyl chain, with fluorination and the sterically hindered substituent contributing to altered binding dynamics. Laboratory synthesis of 5F-ADB generally proceeds via N-alkylation of methyl 1H-indazole-3-carboxylate with 1-bromo-5-fluoropentane in the presence of a , yielding the N-substituted , which is then hydrolyzed to the . The acid is subsequently coupled to (2S)-2-amino-3,3-dimethylbutanoic acid methyl (methyl L-tert-leucinate) using activating agents such as carbonyl diimidazole () or other coupling reagents to form the target carboxamide. This enantiospecific route ensures the S-configuration at the alpha-carbon of the amino acid-derived , as detailed in forensic and pharmacological studies first reporting the compound around 2014.

Physical and Chemical Characteristics

5F-ADB possesses the molecular formula C<sub>20</sub>H<sub>28</sub>FN<sub>3</sub>O<sub>3</sub> and a molecular weight of 377.46 g/mol. In its pure form, it appears as a white crystalline solid. Seized samples often consist of white to off-white powders or oily residues, frequently applied to herbal matrices for distribution. The compound demonstrates in organic solvents including , (DMSO), and (DMF), facilitating its extraction and analysis in laboratory settings. It exhibits low in , which contributes to its typical as a on material rather than aqueous solutions in products. 5F-ADB shows susceptibility to degradation, particularly of its carboxylester moiety under alkaline conditions, elevated temperatures, or prolonged storage at , yielding metabolites that can interfere with forensic detection. Stability is enhanced under frozen conditions, but exposure to heat or non-ideal storage environments accelerates breakdown, complicating in seized materials.

Pharmacology

Mechanism of Action

5F-ADB acts as a full at cannabinoid type 1 (CB1) receptors, G-protein-coupled receptors predominantly expressed in the , mimicking the effects of endogenous like but with substantially greater potency. In fluorometric imaging plate reader assays, it exhibits an EC<sub>50</sub> of 0.59 nM at human CB1 receptors, compared to 171 nM for Δ<sup>9</sup>-THC, indicating approximately 290-fold higher functional potency. This potency arises from its high binding affinity, with Ki values reported in the 0.6-3 nM range, enabling efficient receptor activation and downstream inhibition of , reduction in levels, and modulation of ion channels. The compound demonstrates moderate selectivity for CB1 over CB2 receptors, with a CB2 EC<sub>50</sub> of 7.5 , yielding a selectivity ratio of about 12:1 in favor of CB1. Structural fluorination at the terminal position of the N-pentyl chain enhances and optimizes hydrophobic interactions within the CB1 binding pocket, improving efficiency and metabolic resistance, which prolongs receptor occupancy and signaling compared to non-fluorinated analogs. Ex vivo electrophysiological studies in reveal off-target modulation via CB1 agonism, including activation of firing at concentrations of 1 μM, without direct effects on neurons or involvement of serotonin receptors. This indirect potentiation of underscores the compound's capacity for intense central effects, potentially exacerbating risks of receptor desensitization from sustained high-efficacy activation.

Pharmacokinetics and Metabolism

5F-ADB is predominantly absorbed via , either by plant material impregnated with the compound or vaping e-liquids containing it, leading to rapid pulmonary uptake and onset of psychoactive effects at doses as low as 50 µg. This route provides high due to avoidance of first-pass , with peak effects occurring within minutes based on synthetic administration patterns. The compound undergoes extensive hepatic metabolism primarily through phase I oxidative processes mediated by enzymes in human liver microsomes, exhibiting rapid intrinsic clearance of 256.2 mL min⁻¹ kg⁻¹ and an of 3.1 minutes. Key metabolites include oxidative defluorination (M1), ester hydrolysis (M5 or M7), monohydroxylation of the fluoropentyl chain (M3) or ring (M4), carboxypentyl formation (M2), and combinations thereof, identified in both incubations and authentic human and samples. Several metabolites, including and M5/M7, retain high affinity and full agonist efficacy at CB₁ receptors, comparable to or exceeding the parent compound, which may extend the duration of cannabimimetic effects beyond the short of 5F-ADB itself. In postmortem analyses, predominates in (concentrations around 0.19 ng/mL), while the parent and metabolites distribute preferentially to lipophilic tissues such as adipose (up to 7.95 ng/g) and heart muscle, suggesting potential for tissue accumulation with repeated dosing. This persistence of active metabolites contrasts with natural cannabinoids like THC, where principal metabolites lack significant receptor activity, and may underlie cumulative toxicity risks from frequent use.

History and Development

Discovery and Initial Identification

5F-ADB was first identified in November 2014 in postmortem samples obtained from a 34-year-old man in who died after inhaling smoke from an herbal product. This detection occurred amid a cluster of approximately 10 fatalities reported since late September 2014, where victims experienced unexplained overdoses following use of similar herbal blends marketed as legal alternatives to . Forensic analysis involved extraction from stomach contents, solid tissues, and herbal products, followed by quantitation revealing concentrations up to 67.2 ng/g in gastric contents and 2.3 ng/g in the liver. The compound's structure was elucidated using gas chromatography-mass spectrometry (GC-MS) for initial screening and confirmation of molecular ions, supplemented by (NMR) to resolve its carboxamide core with a 5-fluoropentyl at the N1 position, distinguishing it from earlier indazoles like AB-FUBINACA, which feature a fluorobenzyl rather than fluoropentyl substitution. This fluorinated variant represented a structural modification aimed at circumventing detection and existing regulatory controls on prior . No records indicate prior pharmaceutical research or development for 5F-ADB, positioning its emergence solely within the context of clandestine production for recreational herbal products.

Emergence in Synthetic Cannabinoid Markets

5F-ADB, chemically known as methyl 2-[1-(5-fluoropentyl)indazole-3-carboxamido]-3,3-dimethylbutanoate, first appeared on the European illicit drug market in September 2014, with detections reported in multiple member states by 2015. This indazole-based synthetic cannabinoid proliferated rapidly as producers modified structures from earlier compounds like ADB-PINACA to circumvent emerging controls on naphthoyl and benzoyl indoles, reflecting a pattern of iterative chemical innovation in response to regulatory pressures. By 2016, it had gained significant traction in countries such as Germany, where it became one of the predominant synthetic cannabinoids in seized herbal products until its national scheduling in July of that year. In the United States, 5F-ADB emerged concurrently around 2015-2016, often incorporated into products mimicking through application via solvents onto inert plant substrates like leaves or synthetic fibers, marketed under brand names akin to "" or "K2." Law enforcement seizures during this period frequently revealed admixtures with other , such as FUB-AMB or 5F-APINACA, demonstrating producers' strategies to dilute potency or evade detection by varying compositions post-scheduling of precursors. These mixtures underscored the adaptive dynamics of underground markets, where structural analogs were prioritized to maintain availability amid blanket prohibitions on cannabis-derived THC. The compound's market entry lacked any endorsement for therapeutic or research applications, positioning it exclusively within recreational contexts as a legal to restrictions in jurisdictions with strict prohibitions. This development aligned with broader critiques that prohibitionist frameworks inadvertently spur the creation of more hazardous, untested analogs by incentivizing clandestine synthesis over regulated natural alternatives. Empirical seizure data from 2015 onward highlighted its role in sustaining demand for potent, low-cost euphorics, with producers exploiting minor fluorination or carboxamide tweaks to prolong market viability before successive bans.

Use and Effects

Patterns of Recreational Use

5F-ADB is primarily consumed via , with users it after spraying onto dried material in herbal blends resembling products or vaping it in e-liquids for electronic cigarettes. These preparations exploit perceptions of cannabis-like effects while circumventing prohibitions on natural marijuana, often sold as "" or similar unnamed mixtures targeting individuals avoiding detection in standard drug tests. Its extreme potency necessitates microgram-level doses, with psychoactive effects reported from as little as 50 micrograms when smoked on cigarettes or herbal buds, rendering precise self-dosing challenging in unregulated products. Consumption frequently occurs unknowingly, as 5F-ADB adulterates commercial e-liquids or herbal blends, leading to variable concentrations that heighten overdose risks. Case reports document use among young males, including adolescents aged 14–21 and adults up to their 50s, often in recreational or high-risk contexts such as prisons or among polydrug users. reveals frequent co-ingestion with substances like or other , amplifying hazards through synergistic toxicity in smoked mixtures. The compound's appeal stems from low production costs and temporary legal availability as a analog, though inconsistent dosing in street formulations undermines controlled use.

Subjective and Physiological Effects

5F-ADB elicits subjective effects akin to those of Δ⁹-tetrahydrocannabinol (THC) in preclinical drug discrimination studies, where it fully generalized to THC in rats, indicating overlapping discriminative stimulus properties such as altered perception and intoxication. Human reports, primarily from intoxication cases rather than controlled settings, describe intense euphoria, relaxation, and sensory distortions mimicking but with amplified potency due to its full agonism at cannabinoid receptors, potentially leading to greater dissociation or detachment from reality compared to natural THC. Higher doses have been linked to , anxiety, or acute psychosis-like states, distinguishing it from the more moderated entourage effects of phytocannabinoids in . Physiologically, 5F-ADB induces and in exposed individuals, as documented in clinical case reports and outbreak investigations. Common autonomic effects include dry mouth, , and elevated , reflecting CB₁ receptor-mediated sympathomimetic responses. In animal models, it causes short-acting locomotor with a median effective dose (ED₅₀) of 1.1 / in mice, lasting approximately 30 minutes post-administration. These effects onset rapidly via or but subside more abruptly than THC's prolonged profile, attributable to faster and absence of modulating or minor cannabinoids.

Toxicity and Adverse Outcomes

Acute Health Risks

Acute exposure to 5F-ADB, a potent synthetic , has been associated with severe neuropsychiatric and cardiovascular effects in non-fatal intoxications, primarily due to its high binding affinity at CB1 receptors, resulting in effects far exceeding those of natural at equivalent perceived doses. Common symptoms include acute , anxiety, , , and altered mental status, often requiring hospitalization for supportive care such as benzodiazepines and fluids. These manifestations arise from unintended high dosing in adulterated herbal products, where 5F-ADB concentrations can vary widely, crossing overdose thresholds at levels unlike the milligram-scale possible with THC-containing . In a series of five analytically confirmed non-fatal intoxications in involving 5F-ADB (sometimes co-ingested with MMB-2201), patients aged 20-42 presented with diaphoresis, , , drowsiness, and pronounced sympathomimetic signs including heart rates up to 140 bpm and systolic blood pressures exceeding 160 mmHg; one case involved seizures resolving with . Similarly, a case report detailed a 35-year-old male hospitalized after consuming 5F-ADB-laced material, exhibiting panic attacks, irritability, aggression, and transient , with urinary metabolites confirming exposure at levels consistent with recent intake. These episodes highlight the compound's rapid onset and short duration of action, typically peaking within minutes of and lasting 1-4 hours, complicating user dose control. Hallucinations, delirium, and aggressive behavior have also been documented in acute 5F-ADB exposures, often mimicking or acute , with resolution under sedation but potential for from prolonged . Japanese reports from 2015 onward describe hospitalizations for , , and depersonalization following e-cigarette or herbal use, attributing symptoms to 5F-ADB's ester hydrolysis yielding active metabolites that prolong central effects. The discrepancy in potency—5F-ADB's ED50 for locomotor at 1.1 mg/kg in versus cannabis's safer profile—underpins the elevated risk of acute from minor exposure variances in unregulated products.

Documented Fatalities and Case Studies

5F-ADB has been implicated in multiple fatalities, with postmortem confirming its presence in cases across several countries. In , the compound was identified in approximately ten deaths between 2014 and December 2014, primarily linked to of adulterated products. Four of these occurred within a three-week period in , where 5F-ADB was detected in samples from the decedents, suggesting acute as a contributing factor. European monitoring reported 24 deaths associated with 5F-ADB from 2015 to 2017, comprising 16 cases in and 8 in the . A compilation of 43 fatalities involving 5F-ADB documented central blood concentrations of the parent compound ranging from 0.010 to 2.2 ng/mL, with levels reaching 2.0 to 166 ng/mL in peripheral blood; these findings indicate high potency, with dysrhythmia hypothesized as a mechanism for even at low parental concentrations. Three additional deaths were detailed in cases where 5F-ADB co-occurred with other like 5F-PB-22 and AB-CHMINACA, with extrapolated blood levels for related indazoles around 4.1 ng/mL in one instance. Polydrug involvement is prevalent, as seen in fatalities combining 5F-ADB with or , but mono-intoxication deaths have been verified through toxicological exclusion of other agents, attributing outcomes to respiratory or cardiac effects. One series examined five confirmed 5F-ADB cases, including three fatalities—one mono-intoxication driving impairment leading to crash and two polyintoxications—highlighting variable lethality based on dose and context, with no established safe threshold due to inconsistent product purity in illicit sources.

Legal and Regulatory Status

United States Regulations

In December 2016, the (DEA) issued a temporary order under the (CSA), 21 U.S.C. 811(h), placing 5F-ADB into Schedule I effective immediately, alongside five other , due to findings of high abuse potential, lack of accepted medical use, and absence of accepted safety for use under medical supervision. This temporary control, initially set for up to three years, addressed imminent hazards from its distribution in herbal incense products, with extensions granted periodically as the DEA pursued permanent scheduling. The temporary placement transitioned to permanent Schedule I status via a final DEA rule published on January 24, 2020, effective February 24, 2020, after a notice of proposed rulemaking in April 2019 and consideration of public comments. As a Schedule I substance, 5F-ADB is deemed to have no currently accepted medical use in the United States and a lack of accepted safety for use under medical supervision, subjecting it to the strictest federal controls. Federal penalties for offenses involving 5F-ADB align with those for other Schedule I substances: simple possession carries up to one year and a minimum $1,000 fine for first-time offenders, escalating for repeat offenses or larger quantities; distribution or intent to distribute can result in 5–40 years depending on quantity and prior convictions, with mandatory minimums for trafficking. Enforcement has involved DEA-led seizures of synthetic cannabinoid blends containing 5F-ADB, often marketed as "" or herbal products, and prosecutions under the , supplemented by the Analogue Act (21 U.S.C. 813) for structurally similar variants not explicitly named. While sets the baseline, many states impose additional restrictions or broader bans on , leading to varied enforcement landscapes. The scheduling rationale emphasized 5F-ADB's role in emergencies linked to its manufacture and unpredictable potency, prompting controls to curb proliferation despite ongoing emergence of novel analogs that exploit regulatory gaps through chemical modifications.

International Controls and Bans

The European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) first detected 5F-ADB (also known as 5F-MDMB-PINACA) in in 2014 through post-mortem samples associated with synthetic use, prompting early monitoring as a new psychoactive substance (NPS). This identification aligned with rising detections in herbal products marketed as alternatives, leading to risk communications and national bans across several member states by 2015–2016 under NPS frameworks. However, harmonized EU-wide controls lagged, with individual countries like and implementing prohibitions based on reports, while others relied on generic analog laws. Japan enacted a specific ban on 5F-ADB in December 2014, shortly after its emergence in domestic markets linked to severe intoxications and fatalities, reflecting a rapid response to outbreaks of synthetic cannabinoid-related hospitalizations. As a major early producer hub, imposed controls on 5F-ADB as part of broader NPS scheduling in 2015, targeting to curb export-driven proliferation, though enforcement gaps allowed precursor diversification. These national actions preceded fuller international coordination, highlighting variances where producer nations like prioritized supply-side restrictions earlier than consumer markets. The World Health Organization's Expert Committee on Drug Dependence conducted a critical review of 5F-ADB in , recommending its placement under international control due to evidence of abuse potential, dependence, and public health risks from low-dose toxicity. This led to its scheduling in Schedule II of the 1971 UN by late 2018, enabling global treaty obligations for member states to prohibit production, trade, and possession. Despite this, implementation delays in harmonization—spanning four years from initial detections to UN action—facilitated 5F-ADB's spread via online vendors and chemical analogs, underscoring reactive policy limitations over proactive structural bans on scaffolds. As of 2025, 5F-ADB remains controlled in over 100 countries through specific listings or blanket NPS legislation, including the UK's and Australia's analogue provisions, though evasion tactics like "DIY" precursor kits have prompted ongoing amendments. Regional disparities persist, with faster scheduling in nations contrasting slower adoption in parts of and , where generic laws cover it indirectly but enforcement varies. These controls have reduced overt availability in monitored markets post-2018, yet persistent detections in seizures indicate incomplete global suppression.

Analytical Detection

Methods of Identification

Liquid chromatography-tandem mass spectrometry (LC-MS/MS) and gas chromatography-mass spectrometry (GC-MS) serve as the primary techniques for identifying 5F-ADB in forensic samples, including , , and seized plant material, due to their high for trace-level detection. In LC-MS/MS, 5F-ADB is detected via its protonated molecular ion at m/z 378.2, yielding characteristic fragment ions such as m/z 233.1 (5-fluoropentylindazole acylium ion), m/z 145.0 ( moiety), and m/z 289.1, enabling unequivocal identification against reference spectra. GC-MS methods, often employing QuEChERS extraction for or direct analysis for solids, confirm 5F-ADB through retention indices and mass spectra featuring prominent ions at m/z 251 (base peak) and molecular ion clusters around m/z 377-378. These techniques have been empirically validated since initial case reports in 2014-2015, supporting retrospective screening in stored samples. Nuclear magnetic resonance (NMR) provides confirmatory structural analysis for 5F-ADB in bulk powders or extracts from seized materials, matching proton and signals to the core, 5-fluoropentyl chain, and tert-leucyl carboxamide substituents. Standard immunoassays exhibit limited with 5F-ADB owing to its structural divergence from Δ9-tetrahydrocannabinol, often yielding false negatives and necessitating confirmation for accurate detection. High-resolution variants like LC-QTOF- further enhance identification by exact mass measurement, distinguishing isomers and metabolites in complex matrices.

Challenges in Forensic Analysis

The forensic analysis of 5F-ADB is hindered by its rapid metabolism and chemical instability, which result in extremely low postmortem concentrations, typically ranging from 0.01 to 2.2 ng/mL (median 0.34 ng/mL) in central samples. These trace levels, often below the detection thresholds of routine screening panels, increase the risk of false-negative results unless highly sensitive techniques like chromatography-high-resolution are employed with targeted inclusion of 5F-ADB. Such instability contributes to underreporting of 5F-ADB involvement in fatalities, as the compound degrades post-collection or during biological processing, masking its presence in non-specific assays. Further complications arise from 5F-ADB's into multiple active and variable phase I , such as products, which retain pharmacological activity but vary in detectability across individuals due to differences in hepatic activity. Quantifying exposure becomes challenging because parent compound levels are minimal while predominate, requiring comprehensive profiling to distinguish 5F-ADB from structurally similar ; failure to monitor these can lead to misattribution or overlooked cases. In instances where initial screening yields negatives for the parent, subsequent confirmation has revealed involvement, underscoring the need for multi-tiered analytical strategies. The designer nature of 5F-ADB exacerbates these issues, as its emergence and structural modifications demand continual updates to forensic databases and testing protocols, exposing inefficiencies in static screening regimes that prioritize legacy substances over analogs. Adulteration in recreational products, often containing inconsistent mixtures of , further promotes false negatives in biological samples unless seizures prompt retrospective targeted testing; without such alerts, routine overlooks 5F-ADB, perpetuating underreporting. This dynamic landscape highlights the limitations of broad-spectrum immunoassays, which frequently miss low-potency detections without prior intelligence on circulating variants.