Mirtazapine

Mirtazapine	Last updated: 11/09/2025
(Not known by any other names)

GENERAL INFORMATION

Description

A veterinary substance which is a noradrenergic and specific serotonergic antidepressant (NaSSA)

Examples of veterinary uses

Mainly used to manage anorexia and behavioral disorders in domestic pets

Examples of species treated

Dogs; Cats

Approval status

VMR 2013/2033 approval status (GB/UK)

Approved - usually supplied as a prescription only medicine to be authorised by a veterinarian (POM-V)

EU Regulatory approval status

Approved

Chemical structure

Isomerism

Mirtazapine exhibits stereoisomerism, specifically chirality, due to the presence of a chiral centre in its molecular structure. This means it exists as two enantiomers. Although mirtazapine is typically administered as a racemic mixture, studies suggest that the individual enantiomers may differ in their pharmacological activity.

Chemical formula

C₁₇H₁₉N₃

Canonical SMILES

CN1CCN2C(C1)C3=CC=CC=C3CC4=C2N=CC=C4

Isomeric SMILES

No data

International Chemical Identifier key (InChIKey)

RONZAEMNMFQXRA-UHFFFAOYSA-N

International Chemical Identifier (InChI)

InChI=1S/C17H19N3/c1-19-9-10-20-16(12-19)15-7-3-2-5-13(15)11-14-6-4-8-18-17(14)20/h2-8,16H,9-12H2,1H3

2D structure diagram/image available?

Yes

General status

Veterinary substance type

Medicinal drug: antidepressant

Substance groups

Piperazino-azepine

Minimum active substance purity

Known relevant impurities

Substance origin

Synthetic

Mode of action

Acts as an antagonist at central pre-synaptic alpha(2)-receptors, inhibiting negative feedback to the presynaptic nerve and causing an increase in NE release.

Molecular targets

[5-hydroxytryptamine receptor 2A, Antagonist], [5-hydroxytryptamine receptor 3A, Antagonist], [Alpha-2A adrenergic receptor, Antagonist], [5-hydroxytryptamine receptor 2C, Antagonist], [Kappa-type opioid receptor, Agonist], [Histamine H1 receptor, Antagonist], [Histamine H1 receptor, Unknown action]

CAS RN

61337-67-5

EC number

288-060-6

CIPAC number

US EPA chemical code

PubChem CID

Therapeutic Class

Antidepressant: Psychoanaleptics

ATCvet Code

QN06AX11

Controlled Drug?

Regulation 37/2010 MRL Classification

Molecular mass

265.35

PIN (Preferred Identification Name)

(±)-2-methyl-1,2,3,4,10,14b-hexahydropyrazino(2,1-a)pyrido(2,3-c)(2)benzazepine

IUPAC name

(±)-2-methyl-1,2,3,4,10,14b-hexahydropyrazino(2,1-a)pyrido(2,3-c)(2)benzazepine

CAS name

Forever chemical

Other status information

Relevant Environmental Water Quality Standards

Physical state

Cream to white coloured powder

Commercial

Property

Value

Availability status

Current

Introduction & key dates

1966, introduced USA

Example manufacturers & suppliers of products using this active now or historically

Mirataz Transdermal Ointment

Example products using this active

Dechra Ltd

Formulation and application details

Usually supplied as a topical formulation

Commercial production

The production of mirtazapine involves a multi-step chemical synthesis centred around the cyclisation of a key intermediate compound. The process begins with 2-(4-methyl-2-phenylpiperazin-1-yl)pyridine-3-methanol, which undergoes cyclization using concentrated sulphuric acid to form the tetracyclic structure characteristic of mirtazapine. This reaction mixture is then diluted with water and alkalinized, typically in the presence of propanol, which facilitates the extraction of mirtazapine into the organic phase. The compound is subsequently crystallized from the propanol extract, yielding high-purity mirtazapine suitable for pharmaceutical use. This method ensures efficient isolation and minimizes impurities, making it a reliable route for industrial-scale production.

Impact on climate of production and use

Published GHG data is not available for most pharmaceuticals. However, according to industry, global averages suggest producing 1 kg of a typical active pharmaceutical ingredient can range from 10 to 100 kg CO₂e for small molecule drugs and potentially up to 1000 kg CO₂e for complex biologicals such as vaccines, depending on the drug type, its formulation, complexity of synthesis, solvent recovery, and energy sources used.

ENVIRONMENTAL FATE

Property

Value

Source; quality score; and other information

Interpretation

Solubility - In water at 20 °C (mg l⁻¹)

1.1

Low

Solubility - In organic solvents at 20 °C (mg l⁻¹)

Melting point (°C)

114

Boiling point (°C)

Degradation point (°C)

Flashpoint (°C)

Octanol-water partition coefficient at pH 7, 20 °C

7.94 X 10⁰²

Calculated

Log P

2.9

Moderate

Fat solubility of residues

Solubility

Data type

Density (g ml⁻¹)

Dissociation constant pKa) at 25 °C

Vapour pressure at 20 °C (mPa)

Henry's law constant at 25 °C (Pa m³ mol⁻¹)

Volatilisation as max % of applied dose lost

From plant surface

From soil surface

Maximum UV-vis absorption L mol⁻¹ cm⁻¹

Surface tension (mN m⁻¹)

Refractive Index

Environmental release

Degradation

Property

Value

Source; quality score; and other information

Interpretation

Soil degradation (days) (aerobic)

DT₅₀ (typical)

DT₅₀ (lab at 20 °C)

DT₅₀ (field)

DT₉₀ (lab at 20 °C)

DT₉₀ (field)

Note

Manure DT₅₀ (days)

Aqueous photolysis DT₅₀ (days) at pH 7

Value

Note

Aqueous hydrolysis DT₅₀ (days) at 20 °C and pH 7

Value

Note

Water-sediment DT₅₀ (days)

Water phase only DT₅₀ (days)

Sediment phase only DT₅₀ (days)

Air degradation

As this parameter is not normally measured directly, a surrogate measure is used: ‘Photochemical oxidative DT₅₀’. Where data is available, this can be found in the Fate Indices section below.

Decay in stored produce DT₅₀

Soil adsorption and mobility

Property

Value

Source; quality score; and other information

Interpretation

Linear

K_d (mL g⁻¹)

K_oc (mL g⁻¹)

Notes and range

Freundlich

K_f (mL g⁻¹)

K_foc (mL g⁻¹)

¹/_n

Notes and range

pH sensitivity

Fate indices

Property

Value

Source; quality score; and other information

Interpretation

GUS leaching potential index

Bio-concentration factor

BCF (l kg⁻¹)

CT₅₀ (days)

Known metabolites

None

ECOTOXICOLOGY

Terrestrial ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

320

Rat

Moderate

Mammals - Short term dietary NOEL

(mg kg⁻¹)

(ppm diet)

Mammals - Chronic 21d NOAEL (mg kg⁻¹ bw d⁻¹)

Birds - Acute LD₅₀ (mg kg⁻¹)

Birds - Short term dietary (LC₅₀/LD₅₀)

Birds - Chronic 21d NOEL (mg kg⁻¹ bw d⁻¹)

Earthworms - Acute 14 day LC₅₀ (mg kg⁻¹)

Earthworms - Chronic NOEC, reproduction (mg kg⁻¹)

Soil micro-organisms

Collembola

Acute LC₅₀ (mg kg⁻¹)

Chronic NOEC (mg kg⁻¹)

Non-target plants

Vegetative vigour ER₅₀ (g ha⁻¹)

Seedling emergence ER₅₀ (g ha⁻¹)

Honeybees (Apis spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Unknown mode acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Chronic

Notes

Bumblebees (Bombus spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Mason bees (Osmia spp.)

Contact acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Oral acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg bee⁻¹)

Other bee species (1)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Other bee species (2)

Acute LD₅₀ (worst case from 24, 48 and 72 hour values - μg insect⁻¹)

Mode of exposure

Beneficial insects (Ladybirds)

Beneficial insects (Lacewings)

Beneficial insects (Parasitic wasps)

Beneficial insects (Predatory mites)

Beneficial insects (Ground beetles)

Aquatic ecotoxicology

Property

Value

Source; quality score; and other information

Interpretation

Temperate Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

6.92

Pimephales promelas

Moderate

Temperate Freshwater Fish - Chronic 21 day NOEC (mg l⁻¹)

Tropical Freshwater Fish - Acute 96 hour LC₅₀ (mg l⁻¹)

Temperate Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

19.9

Daphnia magna

Moderate

Temperate Freshwater Aquatic invertebrates - Chronic 21 day NOEC (mg l⁻¹)

0.24

Daphnia magna

Moderate

Tropical Freshwater Aquatic invertebrates - Acute 48 hour EC₅₀ (mg l⁻¹)

Aquatic crustaceans - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Acute 96 hour LC₅₀ (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, static, water (mg l⁻¹)

Sediment dwelling organisms - Chronic 28 day NOEC, sediment (mg kg⁻¹)

Aquatic Plants (free-floating, fonds growth, fresh) - 7 day (mg l⁻¹)

Aquatic plants (rooted, growth rate, fresh) - 14 day (mg l⁻¹)

Algae - Acute (growth rate, fresh; mg l⁻¹)

Algae - Chronic (growth rate, fresh; mg l⁻¹)

Mesocosm study data

NOEAEC mg l⁻¹

Marine bivalves

HUMAN HEALTH AND PROTECTION

General

Property

Value

Source; quality score; and other information

Interpretation

Threshold of Toxicological Concern (Cramer Class)

Mammals - Acute oral LD₅₀ (mg kg⁻¹)

320

Rat

Moderate

Mammals - Dermal LD₅₀ (mg kg⁻¹ body weight)

Mammals - Inhalation LC₅₀ (mg l⁻¹)

Other Mammal toxicity endpoints

ADI - Acceptable Daily Intake (mg kg⁻¹ bw day⁻¹)

ARfD - Acute Reference Dose (mg kg⁻¹ bw day⁻¹)

AAOEL - Acute Acceptable Operator Exposure Level (mg kg⁻¹ bw day⁻¹)

AOEL - Acceptable Operator Exposure Level - Systemic (mg kg⁻¹ bw day⁻¹)

Dermal penetration studies (%)

Dangerous Substances Directive 76/464

Exposure Routes

Public

Occupational

Mammalian dose elimination route and rate

Mirtazapine is extensively metabolized and eliminated via the urine

Health issues

Specific human health issues

Carcinogen

Genotoxic

Endocrine disruptor

No data found

; ; ; ;

Reproduction / development effects

Acetyl cholinesterase inhibitor

Neurotoxicant

No data found

Respiratory tract irritant

Skin irritant

Skin sensitiser

No data found

Eye irritant

Phototoxicant

No data found

General human health issues

Possible CNS toxicant
May cause drowsiness, dry mouth, nausea, diarrhoea and insomnia
Bone marrow depression has been reported

Handling issues

Property

Value and interpretation

General

No information available

CLP classification 2013

WHO Classification

Not listed (Not listed)

UN Number

Waste disposal & packaging

Shelf-life, storage, stability and reactivity

TRANSLATIONS

Language

Name

English

mirtazapine

French

German

Danish

Italian

Spanish

mirtazapina

Greek

Polish

Swedish

Hungarian

Dutch

Norwegian

Record last updated:	11/09/2025
Contact:	aeru@herts.ac.uk
Please cite as:	Lewis, K.A., Tzilivakis, J., Warner, D. and Green, A. (2016) An international database for pesticide risk assessments and management. Human and Ecological Risk Assessment: An International Journal, 22(4), 1050-1064. DOI: 10.1080/10807039.2015.1133242