Mirtazapine versus megestrol acetate in treatment of anorexia-cachexia in advanced cancer patients: a randomized, double-blind trial.

OBJECTIVE: Cancer-related anorexia-cachexia comprises one of the most common syndromes of advanced cancer patients. The management of cancer-related anorexia-cachexia is a great challenge in clinical practice. There are no definite practice guidelines yet for the prevention and treatment of cancer-related anorexia-cachexia. This study is considered to find out whether there is any role of mirtazapine in the improvement of anorexia in cancer patients. METHODS: A total of 80 cancer-anorexia patients were enrolled. Patients in the trial arm received the standard chemotherapy medication plus one tablet of mirtazapine 15 mg daily at night orally for 8 weeks starting from the day of an initial assessment. The control arm received the standard chemotherapy medication plus one tablet of megestrol acetate 160 mg daily orally for 8 weeks starting from the day of an initial assessment. Each patient was assessed by validated versions of Functional Assessment of Anorexia/Cachexia Therapy Anorexia/Cachexia Sub Scale v 4 questionnaires. RESULTS: After 4 and 8 weeks each patient was evaluated again using the Functional Assessment of Anorexia/Cachexia Therapy Anorexia/Cachexia Sub Scale tool. The quality of life of each patient was assessed by European Organization for Research and Treatment QLQ-C30 v 3.0. After 4 to 8 weeks of treatment, the Functional Assessment of Anorexia/Cachexia Therapy Anorexia/Cachexia Sub Scale score in cancer anorexia patients in the mirtazapine improved anorexia significantly. However, the improvement after 4 to 8 weeks was not statistically significant when it was compared with the megestrol acetate (P > 0.05). CONCLUSIONS: Therefore, the findings of this study reveal that mirtazapine might be a potential alternative to megestrol acetate, as it has shown potential efficacy as like as megestrol acetate.

Effects of transdermal mirtazapine on hyporexic rhesus and cynomolgus macaques (Macaca mulatta and Macaca fascicularis).

BACKGROUND: Hyporexia and weight loss are important indicators of physical and psychological well-being in macaque colonies. An FDA-approved transdermal formulated Mirtazapine (MTZ) shows effectiveness in managing feline hyporexia. This study sought to determine its effectiveness as an appetite stimulant in macaques. METHODS: Fourteen macaques with idiopathic hyporexia, intractable to conventional management were treated with transdermal MTZ (0.5 mg/kg) topically administered to aural pinnae once daily for 14 days. Qualitative food consumption was monitored daily for 6 months. Body weights were collected prior to treatment, every 2 weeks for the first 6 weeks, 10 weeks, and 6 months post-treatment. RESULTS: Transdermal MTZ significantly reduced the frequency of hyporexia during treatment and monthly for 6 months. No significant increase in weight noted until approximately 6 months post-treatment. CONCLUSIONS: Results from this study indicate that a short course of transdermal MTZ is an effective way to increase food consumption in macaques chronically.

Antiplatelet Effect of Mirtazapine via Co-blocking of the 5-HT2A and α2-Adrenergic Receptors on Platelets.

Mirtazapine (MTZ) is a noradrenergic and specific serotonergic antidepressant. MTZ is reportedly associated with an increased risk of bleeding. However, the underlying mechanism remains unclear. In this study, we investigated the antiplatelet effect of MTZ in mice via light transmission aggregometry to elucidate the mechanism of MTZ-induced bleeding. The results of the ex vivo study showed that the oral administration of MTZ (20 or 100 mg/kg) significantly suppressed platelet aggregation mediated by the synergic interaction of 5-hydroxytryptamine (5-HT) and adrenaline. Additionally, MTZ significantly suppressed platelet aggregation, mediated by the synergic interaction of ADP and 5-HT or adrenaline. Similar results were obtained in vitro, under the condition of 5-HT- and adrenaline-induced platelet aggregation. Overall, the results suggest that MTZ exerts antiplatelet effect by co-blocking 5-HT2A and α2-adrenergic receptors on platelets and suppresses platelet aggregation mediated by ADP, increased by either 5-HT or adrenaline. Thus, a detailed monitoring of bleeding is recommended for patients taking MTZ.

Mirtazapine, an α2 Antagonist-Type Antidepressant, Reverses Pain and Lack of Morphine Analgesia in Fibromyalgia-Like Mouse Models.

Treatment of fibromyalgia is an unmet medical need; however, its pathogenesis is still poorly understood. In a series of studies, we have demonstrated that some pharmacological treatments reverse generalized chronic pain but do not affect the lack of morphine analgesia in the intermittent cold stress (ICS)-induced fibromyalgia-like pain model in mice. Here we report that repeated intraperitoneal treatments with mirtazapine, which is presumed to disinhibit 5-hydroxytriptamine (5-HT) release and activate 5-HT1 receptor through mechanisms of blocking presynaptic adrenergic α2 and postsynaptic 5-HT2 and 5-HT3 receptors, completely reversed the chronic pain for more than 4 to 5 days after the cessation of treatments. The repeated mirtazapine treatments also recovered the morphine analgesia after the return of nociceptive threshold to the normal level. The microinjection of small interfering RNA (siRNA) adrenergic α2a receptor (ADRA2A) into the habenula, which showed a selective upregulation of α2 receptor gene expression after ICS, reversed the hyperalgesia but did not recover the morphine analgesia. However, both reversal of hyperalgesia and recovery of morphine analgesia were observed when siRNA ADRA2A was administered intracerebroventricularly. As the habenular is reported to be involved in the emotion/reward-related pain and hypoalgesia, these results suggest that mirtazapine could attenuate pain and/or augment hypoalgesia by blocking the habenular α2 receptor after ICS. The recovery of morphine analgesia in the ICS model, on the other hand, seems to be mediated through a blockade of α2 receptor in unidentified brain regions. SIGNIFICANCE STATEMENT: This study reports possible mechanisms underlying the complete reversal of hyperalgesia and recovery of morphine analgesia by mirtazapine, a unique antidepressant with adrenergic α2 and serotonergic receptor antagonist properties, in a type of intermittently repeated stress (ICS)-induced fibromyalgia-like pain model. Habenula, a brain region which is related to the control of emotional pain, was found to play key roles in the antihyperalgesia, whereas other brain regions appeared to be involved in the recovery of morphine analgesia in the ICS model.

Mirtazapine reduces the expression of cocaine-induced locomotor sensitization in male and female Wistar rats.

BACKGROUND: Epidemiological studies have described that women are more vulnerable to the reinforcing effects of cocaine. In animals, the findings are similar: female rats show higher levels of cocaine self-administration and increased cocaine-induced locomotor activity. In contrast, women with depression respond better to treatment with antidepressants, however their therapeutic response to tetracyclic antidepressants is lower. Several studies have shown that mirtazapine-a tetracyclic antidepressant-decreases the behavioral effects of cocaine in male rats. The objective of this study was to evaluate the efficacy of daily dosing of mirtazapine on cocaine-induced locomotor activity and sensitization in naive female rats compared to male rats. METHODS: Male and female Wistar rats were daily dosed with 10 mg/kg of cocaine. During extinction, cocaine was withdrawn and the groups received daily mirtazapine (30 mg/kg, i.p.) or saline. Tamoxifen was administered during the antagonism phase. After each administration, locomotor activity for each animal was recorded for 30 min in transparent Plexiglass activity chambers. RESULTS: In this study, a higher cocaine locomotor response was found in females than in males and the mirtazapine was equally effective in decreasing cocaine-induced locomotor activity and the expression of locomotor sensitization in male and female rats. In addition, co-administration of mirtazapine and tamoxifen enhanced the efficacy of mirtazapine in female rats. CONCLUSION: The results suggest that mirtazapine may be considered an effective therapeutic option for the treatment of cocaine use disorder in men and women.

No benefit from flexible titration above minimum licensed dose in prescribing antidepressants for major depression: systematic review.

BACKGROUND: In fixed-dose antidepressant trials, the lower range of the licensed dose achieves the optimal balance between efficacy and tolerability. Whether flexible upward titration while side-effects permit provides additional benefits is unknown. METHODS: We did a systematic review of placebo-controlled randomized trials that examined selective serotonin reuptake inhibitors (SSRIs), venlafaxine or mirtazapine in the acute treatment of major depression. Our primary outcome was response, defined as 50% or greater reduction in depression severity. Secondary outcomes included drop-outs due to adverse effects and drop-outs for any reason. We conducted random-effects meta-analyses to calculate the ratios of odds ratios (RORs) between trials comparing the flexible dose titrating above the minimum licensed dose against placebo and those comparing the fixed minimum licensed dose against placebo. RESULTS: We included 123 published and unpublished randomized controlled trials (29 420 participants). There was no evidence supporting efficacy of the flexible dosing over the fixed low dose of SSRIs (ROR 0.96, 95% CI: 0.73 to 1.25), venlafaxine (1.24, 0.96 to 1.60) or mirtazapine (0.77, 0.33 to 1.78). No important differences were noted for tolerability or for any subgroup analyses except the superior efficacy of venlafaxine flexible dosing between 75 and 150 mg over the fixed 75 mg (1.30, 1.02 to 1.65). CONCLUSION: There was no evidence to support added value in terms of efficacy, tolerability or acceptability of flexibly titrating up the dosage over the minimum licensed dose of SSRIs or mirtazapine. For venlafaxine, increased efficacy can be expected by flexibly titrating up to 150 mg.

Methods for constructing treatment episodes and impact on exposure-outcome associations.

PURPOSE: To assess the impact on exposure time and outcome misclassifications, and consequent impact on exposure-outcome associations from treatment episode construction. We investigated the dosage assumptions of 1 unit per day, and 1 DDD per day, versus actual prescribed dosage under different handling of gaps and overlaps of prescriptions. METHODS: Data on mirtazapine and citalopram exposure (years 2006-2014) from the Swedish Prescribed Drug register were used. Via a within individuals design we compared method A, based on actual dosage, with methods B and C based on 1 unit of drug per day and 1 DDD per day assumptions, respectively, including consideration of gaps and overlaps. Four outcomes were used, hospitalizations and outpatient visits for all and for psychiatric causes. RESULTS: Relative to method A, both alternative methods lead to misclassification of exposure time. With regard to outcome misclassifications, method B overestimates the effect of the exposure on the outcome in 77% and 100% of exposure definition comparisons for mirtazapine and citalopram respectively, while 23% of the comparisons for mirtazapine results in underestimation of exposure-outcome associations. Conversely, treatment episodes based on DDD (method C) result in underestimation of the exposure-outcome association in 100% and 87.5% of exposure definition comparisons for mirtazapine and citalopram respectively, while 12.5% of the comparisons for citalopram results in overestimation of the exposure-outcome associations. CONCLUSIONS: The study provides results that have consistent clinical relevance. We have showed that a non-accurate construction of exposure time may lead to errors on outcome detection during exposed time, and consequently affect conclusions on safety or efficacy profile of a treatment.

What is the evidence for mirtazapine in treating cancer-related symptomatology? A systematic review.

PURPOSE: Cancer patients often experience multiple distressing symptoms which are challenging to manage. It would therefore be helpful to find a treatment that alleviates more than one symptom, to avoid polypharmacy: mirtazapine has been used in several studies for this purpose. The objective of this study was to assess the effectiveness and safety of mirtazapine in alleviating one or more frequently encountered cancer-related symptoms. METHODS: Systematic review of clinical trials in English or French. Eight databases were searched. Included studies assessed the effectiveness of mirtazapine in alleviating one or more frequently encountered cancer-related symptoms. Comparator and validated assessment tools were required. Studies were independently appraised by two investigators before data synthesis. RESULTS: The search yielded 1898 references, from which we identified 12 relevant articles evaluating highly heterogeneous outcomes. These were two randomised-controlled (RCTs), three non-randomised controlled, and seven non-randomised non-controlled trials. In total, 392 participants were included and 185 were in RCTs. No study assessed the effectiveness of mirtazapine in alleviating symptoms at the same time, but some considered more than one symptom. Overall, the data was of poor quality, limited by small sample size and bias. However, mirtazapine showed effectiveness in treating depression, anxiety, sleep disorders, emesis and neuropathic pain. Across all studies, mirtazapine is safe to use, with drowsiness and dizziness the most common side-effects. CONCLUSION: Study design and small sample sizes limit the ability to interpret results. Trials to assess the impact of mirtazapine or other medicines in alleviating multiple symptoms would be valuable.

Sertraline and Mirtazapine Versus Placebo in Subgroups of Depression in Dementia: Findings From the HTA-SADD Randomized Controlled Trial.

OBJECTIVE: Studies have shown that antidepressants are no better than placebo in treating depression in dementia. The authors examined antidepressant efficacy in subgroups of depression in dementia with different depressive symptom profiles. METHODS: This study focuses on exploratory secondary analyses on the randomized, parallel-group, double-blind, placebo-controlled Health Technology Assessment Study of the Use of Antidepressants for Depression in Dementia (HTA-SADD) trial. The setting included old-age psychiatry services in nine centers in England. The participants included 326 patients meeting National Institute of Neurological and Communicative Disorders and Stroke/Alzheimer's Disease and Related Disorders Association probable/possible Alzheimer disease criteria, and Cornell Scale for Depression in Dementia (CSDD) scores of 8 or more. Intervention was placebo (n = 111), sertraline (n = 107), or mirtazapine (n = 108). Latent class analyses (LCA) on baseline CSDD items clustered participants into symptom-based subgroups. Mixed-model analysis evaluated CSDD improvement at 13 and 39 weeks by randomization in each subgroup. RESULTS: LCA yielded 4 subgroups: severe (n = 34), psychological (n = 86), affective (n = 129), and somatic (n = 77). Mirtazapine, but not sertraline, outperformed placebo in the psychological subgroup at week 13 (adjusted estimate: -2.77 [standard error (SE) 1.16; 95% confidence interval: -5.09 to -0.46]), which remained, but lost statistical significance at week 39 (adjusted estimate: -2.97 [SE 1.59; 95% confidence interval: -6.15 to 0.20]). Neither sertraline nor mirtazapine outperformed placebo in the other subgroups. CONCLUSION: Because of the exploratory nature of the analyses and the small sample sizes for subgroup analysis there is the need for caution in interpreting these data. Replication of the potential effects of mirtazapine in the subgroup of those with depression in dementia with "psychological" symptoms would be valuable. These data should not change clinical practice, but future trials should consider stratifying types of depression in dementia in secondary analyses.

Efficacy and Safety of Appetite-Stimulating Medications in the Inpatient Setting.

BACKGROUND: Hospitalized patients are subject to acute illness and stress which may impact appetite or weight. Loss of appetite may lead to increased morbidity or mortality. Medications such as dronabinol, megestrol, and mirtazapine are used for weight gain in the outpatient setting; however, there is limited information about safety or effectiveness when initiated inpatient. OBJECTIVES: To analyze the effectiveness and safety of appetite-stimulating medications in hospitalized patients. METHODS: This was a retrospective cohort study of hospitalized patients initiated on dronabinol, megestrol, or mirtazapine for appetite. The primary outcome was change in meal intake between drug initiation and discontinuation. Secondary outcomes included documented improvement in appetite, change in weight and various laboratory parameters, and incidence of adverse effects. RESULTS: A total of 38 patients met inclusion criteria, and mirtazapine was most commonly used (42%). There was no significant difference between groups of appetite-stimulating medications with regard to mean change in meal intake, weight, albumin, or documented improvement in diet. Within groups, each agent showed numerical improvement in percentage meal intake, with a mean change from initiation to discontinuation of 17.12%. Almost half (48%) of the patients experienced improvement in diet after the start of medications. No serious adverse effects were observed. Conclusion and Relevance: In inpatients, there was no difference in change in meal intake or weight between dronabinol, megestrol, or mirtazapine, but they may show numerical improvements in meal intake. To our knowledge, this is the first study to evaluate the use of dronabinol, megestrol, and mirtazapine initiated in the inpatient setting.

A double-blind, placebo-controlled, randomized study to evaluate the weight gain drug, mirtazapine transdermal ointment, in cats with unintended weight loss.

Mirtazapine is classified as a weight gain drug in cats, and the purpose of this study was to evaluate its efficacy in cats experiencing unintended weight loss. This was a multi-center, double-blind, placebo-controlled, randomized clinical study in client-owned cats ≥1 year of age, weighing ≥2 kg, with a documented loss (≥5%) in body weight. Cats were treated once daily with either 2 mg/cat mirtazapine transdermal ointment (n = 83) or placebo (n = 94) (Per Protocol population) applied to the inner surface of the pinna for 14 ± 3 days. Physical examination, body weight, complete blood count, serum chemistry, and urinalysis were performed prior to treatment and on Day 14. Changes in body weight between the mirtazapine and placebo groups were evaluated from Day 1 to Day 14 and compared using a two-sample t test. The mean percent change in body weight was +3.9% (standard deviation ±5.4%) in the mirtazapine group and +0.4% (±3.3%) in the placebo group (p < 0.0001). The most common adverse event was mild erythema at the application site in 17.4% of placebo and 10.4% of mirtazapine-treated cats. Application of mirtazapine transdermal ointment was well tolerated both topically and systemically and resulted in significant weight gain in cats experiencing unintended weight loss associated with various underlying diseases.

Combination of mirtazapine and paroxetine: possible clinically demonstrated interaction?

We currently have a wide range of antidepressants available. However, the mechanisms of action are different, giving a theoretical justification for their combination in the failure of monotherapy. However, the combination of drugs entails, in addition to benefits, an increase in the risk of, for example, drug interactions. Many drug interactions in psychiatry are due to the pharmacokinetic interactions between drugs, where their plasma concentrations are altered by inhibiting or inducing cytochrome P450 isoenzymes, especially CYP2D6 and CYP3A4 and P-glycoprotein. When treating depression, we should consider the risks and benefits of combination therapy in individual patients and take measures to minimize the side effects of medicines. The case report describes a case of a patient who reported significant depression after adding paroxetine and mirtazapine to psychiatric medication. As a theoretical cause, it discusses the possible clinically demonstrated interaction between paroxetine and mirtazapine, which has been clinically manifested by fatigue and pronounced daytime sleepiness.

Very Low-Dose Mirtazapine (7.5 mg) in Treatment of Acute Antipsychotic-Associated Akathisia.

BACKGROUND: Some evidence suggests that off-label use of mirtazapine (15 mg) is effective in treatment of acute antipsychotic-associated akathisia (AAA). We analyzed whether a lower dose of mirtazapine (7.5 mg) maintained its antiakathisia properties while exhibiting better tolerability in patients with schizophrenia and mood disorders who developed acute AAA. METHODS: Medical charts were retrospectively evaluated for 12 patients with AAA. All scored at least 2 (mild akathisia) on the Barnes Akathisia Rating Scale (BARS) and were treated with mirtazapine (7.5 mg) for a mean of 10.3 days. RESULTS: There was a statistically significant decrease in the BARS subjective, distress, and global (P < 0.01 to P < 0.001), but not objective (P = 0.63), subscales. Five participants (41.6%) fulfilled the predefined criterion of response, a decrease of at least 2 points on the BARS global subscale. The positive antiakathisia effect of mirtazapine was observed predominantly in aripiprazole-treated patients. Mirtazapine (7.5 mg) was well tolerated, and no clinically significant adverse effects, primarily drowsiness or increased appetite, were reported. CONCLUSIONS: A large-scale controlled evaluation is warranted to substantiate clinical utility of off-label use of mirtazapine (7.5 mg) for patients with AAA.

Discontinuation and dose adjustment of metoprolol after metoprolol-paroxetine/fluoxetine co-prescription in Dutch elderly.

PURPOSE: Co-prescription of paroxetine/fluoxetine (a strong CYP2D6 inhibitor) in metoprolol (a CYP2D6 substrate) users is common, but data on the clinical consequences of this drug-drug interaction are limited and inconclusive. Therefore, we assessed the effect of paroxetine/fluoxetine initiation on the existing treatment with metoprolol on the discontinuation and dose adjustment of metoprolol among elderly. METHODS: We performed a cohort study using the University of Groningen IADB.nl prescription database (www.IADB.nl). We selected all elderly (≥60 years) who had ever been prescribed metoprolol and had a first co-prescription of paroxetine/fluoxetine, citalopram (weak CYP2D6 inhibitor), or mirtazapine (negative control) from 1994 to 2015. The exposure group was metoprolol and paroxetine/fluoxetine co-prescription, and the other groups acted as controls. The outcomes were early discontinuation and dose adjustment of metoprolol. Logistic regression was applied to estimate adjusted odds ratios (OR) and 95% confidence intervals (CI). RESULTS: Combinations of metoprolol-paroxetine/fluoxetine, metoprolol-citalopram, and metoprolol-mirtazapine were started in 528, 673, and 625 patients, respectively. Compared with metoprolol-citalopram, metoprolol-paroxetine/fluoxetine was not significantly associated with the early discontinuation and dose adjustment of metoprolol (OR = 1.07, 95% CI:0.77-1.48; OR = 0.87, 95% CI:0.57-1.33, respectively). In comparison with metoprolol-mirtazapine, metoprolol-paroxetine/fluoxetine was associated with a significant 43% relative increase in early discontinuation of metoprolol (OR = 1.43, 95% CI:1.01-2.02) but no difference in the risk of dose adjustment. Stratified analysis by gender showed that women have a significantly high risk of metoprolol early discontinuation (OR = 1.62, 95% CI:1.03-2.53). CONCLUSION: Paroxetine/fluoxetine initiation in metoprolol prescriptions, especially for female older patients, is associated with the risk of early discontinuation of metoprolol.

Single and multiple dose pharmacokinetics of a novel mirtazapine transdermal ointment in cats.

Single and multiple dose pharmacokinetics (PK) of mirtazapine transdermal ointment applied to the inner ear pinna of cats were assessed. Study 1 was a randomized, cross-over single dose study (n = 8). Cats were treated once with 0.5 mg/kg of mirtazapine transdermal ointment applied topically to the inner ear pinna (treatment) or administered orally (control) and then crossed over after washout. Plasma was collected predose and at specified intervals over 96 hr following dosing. Study 2 was a multiple dose study (n = 8). Cats were treated daily for 14 days with 0.5 mg/kg of mirtazapine transdermal ointment applied topically to the inner pinna. Plasma was collected on Day 13 predose and at specified intervals over 96 hr following the final dose. In Study 1, single transdermal administration of mirtazapine resulted in mean Tmax = 15.9 hr, Cmax = 21.5 ng/mL, AUC0-24 = 100 ng*hr/mL, AUC0-∞ = 260 ng*hr/mL and calculated half-life = 26.8 hr. Single oral administration of mirtazapine resulted in mean Tmax = 1.1 hr, Cmax = 83.1 ng/mL, AUC0-24 = 377 ng*hr/mL, AUC0-∞ = 434 ng*hr/mL and calculated half-life = 10.1 hr. Mean relative bioavailability (F) of transdermal to oral dosing was 64.9%. In Study 2, daily application of mirtazapine for 14 days resulted in mean Tmax = 2.1 hr, Cmax = 39.6 ng/mL, AUC0-24 = 400 ng*hr/mL, AUC0-∞ = 647 ng*hr/mL and calculated half-life = 20.7 hr. Single and repeat topical doses of a novel mirtazapine transdermal ointment achieve measurable plasma concentrations in cats.

Successful treatment for serious depression with suicidal risk in a heart transplant patient.

INTRODUCTION: Major depressive disorder is related to unfavourable outcomes in patients with severe comorbidities. In transplant patients, major depression is associated with worse clinical outcomes. CASE REPORT: We present the case of a 55-year-old man with a heart transplant due to heart failure of ischaemic origin. Six months after the transplant he developed depressed mood, anhedonia and suicidal ideation with a score of 20/27 on the PHQ-9 depression screening scale. After receiving mirtazapine 30 mg/night for a week and persisting with a high suicide risk, it was decided to administer ketamine infusion for 24 h, with which a significant improvement in mood was observed, and the disappearance of suicidal ideation 24 h after the infusion. DISCUSSION: Depression in transplant patients is a factor associated with graft loss and post-transplant mortality, in addition to favouring other negative outcomes such as deep vein thrombosis. CONCLUSIONS: Ketamine infusion was shown to be an effective and safe option to treat major depression with suicidal risk in a heart transplant patient.

Mirtazapine to alleviate severe breathlessness in patients with COPD or interstitial lung diseases (BETTER-B): an international, multicentre, double-blind, randomised, placebo-controlled, phase 3 mixed-method trial.

BACKGROUND: Breathlessness frequently becomes severe among people with respiratory disease. Mirtazapine, a widely used antidepressant, has shown promise in the modulation of respiratory sensation and the response to it, as well as reducing feelings of panic, which often accompanies breathlessness. We aimed to determine the effectiveness of mirtazapine to alleviate severe persisting breathlessness. METHODS: This international, multicentre, phase 3, parallel-group, double-blind, randomised, placebo-controlled trial across 16 centres in seven countries (Australia, Germany, Ireland, Italy, New Zealand, Poland, and the UK), recruited adults with chronic obstructive pulmonary disease (COPD), interstitial lung diseases, or both, and grade 3 or 4 of the modified Medical Research Council breathlessness scale. Consenting participants were randomly assigned (1:1) to receive oral mirtazapine or matching placebo for 56 days. Randomisation was by minimisation. The initial mirtazapine dose was 15 mg, escalating to a maximum of 45 mg per day, tapered at treatment end. Participants, caregivers, assessors, and investigators were masked to group assignment. The primary outcome was worst breathlessness in the preceding 24 h measured on a 0-10 numerical rating scale (NRS), at 56 days post-treatment start, with follow-up to 180 days. The primary analysis was performed in the modified intention-to-treat population using multivariable multi-level repeated measures model. This trial was registered with ISRCTN (ISRCTN10487976 and ISRCTN15751764 [Australia and New Zealand]) and EudraCT (2019-002001-21) and is complete. FINDINGS: Between Feb 4, 2021 and March 28, 2023, we enrolled 225 eligible participants (148 men and 77 women, 113 to the mirtazapine group and 112 to the placebo group). The median age was 74 years (IQR 67-78). No evidence of a difference was found in worst breathlessness at day 56 between mirtazapine and placebo (difference in adjusted mean NRS score was 0·105 [95% CI -0·407 to 0·618]; p=0·69). Although the study was underpowered, the primary endpoint effect did not reach the pre-specified treatment effect of 0·55 for worst breathlessness score reduction that the study was powered to detect for the primary analysis. There were 215 adverse reactions in 72 (64%) of 113 participants in the mirtazapine group versus 116 in 44 (40%) of 110 participants in the placebo group; 11 serious adverse events in six (5%) participants in the mirtazapine group versus eight in seven (6%) participants in the placebo group; and one (1%) suspected unexpected serious adverse reaction in the mirtazapine group. At day 56, there were three deaths in the mirtazapine group and two deaths in the placebo group. At day 180, there were seven deaths in the mirtazapine group and 11 deaths in the placebo group. INTERPRETATION: Our findings suggested that mirtazapine of doses 15 to 45 mg daily over 56 days does not improve severe breathlessness among patients with COPD or interstitial lung diseases and might cause adverse reactions. Based on these findings, we do not recommend mirtazapine as a treatment to alleviate severe breathlessness. FUNDING: EU Horizon 2020 (grant agreement No. 825319); Cicely Saunders International Breathlessness Programme; National Institute for Health and Care Research Applied Research Collaboration South London; Australian National Health and Medical Research Council-EU (application ID: APP1170731).