Key Facts

Novel psychoactive substances represent a rapidly evolving challenge for healthcare. Hundreds of new compounds emerge each year, often with limited pharmacological data. Clinical presentations can be severe and unpredictable. Healthcare professionals must recognise common toxidromes and provide appropriate supportive care.

Epidemiology

• >800 NPS identified by the European Monitoring Centre for Drugs and Drug Addiction (EMCDDA) since 2005
• Prevalence of past-year NPS use in UK: approximately 0.5-1% of 16-59 year olds
• Synthetic cannabinoids: most commonly used NPS; concentrated in homeless and prison populations (prevalence up to ~90% in some prison surveys)
• NPS-related deaths: increasing; ~200/year in England and Wales (often involving novel benzodiazepines)
• Mephedrone: was most popular NPS before classification as Class B in 2010

Aetiology — Major NPS Categories

1. Synthetic cannabinoid receptor agonists (SCRAs): Spice, Black Mamba, ADB-BUTINACA; full CB1 agonists (much more potent and dangerous than THC, which is a partial agonist)
2. Synthetic cathinones: mephedrone, MDPV, alpha-PVP ("flakka"); monoamine releasers/reuptake inhibitors
3. Novel benzodiazepines: flualprazolam, etizolam, flubromazolam; GABA-A modulators
4. Novel opioids: nitazenes (isotonitazene, metonitazene); extremely potent (some 100-1000× morphine potency)
5. Psychedelic phenethylamines and tryptamines: 2C-B, NBOMe, DMT analogues
6. Dissociatives: methoxetamine, novel PCP analogues; NMDA receptor antagonists

Pathophysiology

• SCRAs: full CB1 receptor agonism → much greater risk of seizures, psychosis, cardiovascular toxicity, and death compared to natural cannabis
• Synthetic cathinones: similar mechanism to amphetamines/MDMA → sympathomimetic and serotonergic toxicity
• Nitazenes: μ opioid receptor agonists with potency exceeding fentanyl → high overdose risk; may require very large naloxone doses
• Novel benzodiazepines: enhanced GABA-A agonism; variable potency and duration; frequently combined with opioids → respiratory depression

Synthetic Cannabinoids (SCRAs)

• Agitation, psychosis: more severe than natural cannabis; paranoia, aggression
• Seizures: generalised tonic-clonic
• Cardiovascular: tachycardia, hypertension, chest pain, myocardial ischaemia
• Bradycardia and hypotension: paradoxically in some compounds
• Acute kidney injury: associated with certain SCRAs
• Coma and respiratory depression: unlike natural cannabis
• Characteristic posturing: "Spice zombies" — cataleptic states in public

Synthetic Cathinones

• Sympathomimetic toxidrome: tachycardia, hypertension, hyperthermia, diaphoresis, mydriasis
• Agitation and paranoia: severe; may require physical restraint and sedation
• Serotonin toxicity: myoclonus, hyperthermia, autonomic instability
• Bruxism, jaw clenching: similar to MDMA
• Hyponatraemia: particularly with MDMA-like compounds (excess water intake + ADH release)

Novel Benzodiazepines

• Sedation and respiratory depression: often severe; potentiates opioid toxicity
• Unpredictable duration: some have very long half-lives
• May not respond to standard flumazenil doses

Nitazenes/Novel Opioids

• Classic opioid toxidrome: miosis, respiratory depression, reduced consciousness
• May require massive naloxone doses (10-20+ mg)
• Prolonged observation required

Red Flags

• Severe hyperthermia >40°C: medical emergency — aggressive cooling, dantrolene
• Seizures: status epilepticus risk with SCRAs
• GCS <8 with apnoea: may be novel opioid or benzodiazepine — trial of naloxone
• Severe agitation with rhabdomyolysis: CK, renal function, aggressive IV fluids
• Hyponatraemia <125 mmol/L: risk of cerebral oedema; restrict fluids, seek specialist advice
• Serotonin syndrome: clinical emergency — cyproheptadine, benzodiazepines, cooling

Bedside

• Observations: HR, BP, temperature, RR, SpO2, GCS — frequent monitoring
• ECG: arrhythmias, QTc prolongation, sodium channel blockade (wide QRS)
• Capillary glucose: exclude hypoglycaemia
• Urine drug screen: standard immunoassay — often negative for NPS; still useful to identify co-ingestants

Bloods

• ABG/VBG: acidosis, lactate, oxygenation
• U&Es: AKI (SCRAs), hyponatraemia (cathinones/MDMA-like compounds)
• CK: rhabdomyolysis (may be massively elevated)
• LFTs: hepatotoxicity (some cathinones)
• FBC: leucocytosis (stress response)
• Coagulation: DIC in severe cases
• Paracetamol and salicylate: routine in acute presentations

Imaging

• CT head: if seizures, focal neurology, prolonged reduced consciousness
• Chest X-ray: if aspiration, pulmonary oedema, or chest pain

Special Tests

• Specialist toxicology screen: liquid chromatography-mass spectrometry (LC-MS/MS) — identifies specific NPS; send via National Poisons Information Service
• TOXBASE/NPIS: contact for guidance on specific substances
• Wedinos: Welsh substance testing service providing information on circulating NPS in UK

Non-pharmacological

• Toxidrome-based approach: identify the predominant clinical picture and manage accordingly
• Calm, safe environment: reduce stimulation for agitated patients
• Active cooling: for hyperthermia >39°C
• IV fluid resuscitation: for dehydration, rhabdomyolysis, hypotension
• Continuous monitoring: in high-dependency setting for severe presentations

Pharmacological

• Sympathomimetic/serotonergic toxidrome (cathinones, stimulant NPS):
  • Diazepam 5-10 mg IV (repeat as needed): first-line for agitation, seizures, cardiovascular complications
  • Active cooling: external methods
  • Cyproheptadine 12 mg PO then 4 mg 2-hourly: for serotonin syndrome
  • Avoid antipsychotics in acute sympathomimetic toxicity (lower seizure threshold, impair thermoregulation)
• Cannabinoid toxidrome (SCRAs):
  • Benzodiazepines for agitation and seizures
  • Standard seizure management: lorazepam 4 mg IV
  • Supportive care; monitor renal function
• Sedative toxidrome (novel benzodiazepines):
  • Airway management: intubation if GCS <8 and airway compromise
  • Flumazenil generally avoided (risk of seizures in chronic benzodiazepine users and mixed ingestions)
  • Supportive monitoring
• Opioid toxidrome (nitazenes, novel opioids):
  • Naloxone: may require very high doses (>10 mg); repeated boluses or infusion
  • Prolonged observation (some nitazenes have long half-lives)

Surgical

• Not routinely applicable; intubation/ventilation for airway protection

Referral Criteria

• ICU/HDU: severe toxicity, refractory seizures, rhabdomyolysis with AKI, respiratory failure
• NPIS/toxicology: contact for specialist advice on unknown substances
• Drug and alcohol services: for ongoing support after acute presentation
• Mental health assessment: if psychosis persists beyond acute intoxication
• Social services: if homelessness, safeguarding concerns

Outcomes

• Most acute NPS presentations: resolve with supportive care within 24-48 hours
• SCRA-related psychosis: usually resolves within days of cessation; may unmask underlying psychotic disorder
• Nitazene overdose: high mortality if naloxone not administered promptly; survivors generally recover
• Rhabdomyolysis with AKI: may require temporary dialysis; most recover renal function

Complications

• Death: NPS-related deaths increasing; novel benzodiazepines + opioids most lethal combination
• Chronic psychotic disorder: may be triggered by repeated SCRA use
• Acute kidney injury: particularly with certain SCRA compounds
• Persistent cognitive impairment: after prolonged SCRA or cathinone use
• Social harms: homelessness, criminalisation, social exclusion

NPS Toxidrome Recognition

UK Regulatory Framework