Mirtazapine for Methamphetamine Addiction: A Breakthrough or Still a Cautious Signal?

by Kaida JIANG

Methamphetamine use disorder remains one of the more difficult problems in addiction medicine. The clinical need is obvious, but the pharmacologic options remain thin. In the trial published in JAMA Psychiatry, the starting point is stated plainly: methamphetamine use disorder is a major global health challenge, and there are still no approved pharmacotherapies for it. That fact alone helps explain why a positive phase 3 medication trial draws attention. But attention is not the same as resolution. The more useful question is whether this study changes the clinical conversation in a durable way, or whether it still belongs in the category of promising but provisional signals.

The answer is somewhere in between. This was not a small, highly selective pilot. It was a phase 3, double-blind, placebo-controlled randomized clinical trial conducted at six outpatient alcohol and other drug clinics in Australia, with 344 adults who had moderate to severe methamphetamine use disorder. Participants received either mirtazapine 30 mg daily or placebo for 12 weeks. The central result was favorable to mirtazapine: the medication produced a greater reduction in methamphetamine use days than placebo, and the trial did not identify unexpected safety concerns. That is meaningful. It is also not the same thing as a breakthrough in the stronger, practice-defining sense.

Introduction

One reason this paper matters is that it addresses a field in which treatment development has repeatedly disappointed. In methamphetamine use disorder, clinicians are often forced to rely on psychosocial care, harm reduction, and persistence rather than on a medication with established efficacy. The study’s own rationale reflects that context: mirtazapine was not introduced here as an arbitrary repurposing exercise, but as a candidate supported by earlier phase 2 trials and enough mechanistic plausibility to justify a larger test.

The paper notes that prior trials had already shown a difference between active treatment and placebo in methamphetamine-positive urine tests, which is why this larger multisite study was undertaken. A positive finding in a larger, multisite phase 3 trial conducted in routine clinical practice is more than interesting. It suggests that the effect may survive outside a tightly curated research environment.

What The Study Actually Tested

The trial enrolled adults aged 18 to 65 years who had moderate to severe methamphetamine use disorder in the past year, had used methamphetamine at least twice weekly in the previous four weeks, and had a positive drug screen for amphetamines at entry. The study ran between November 2022 and May 2025 at six outpatient government-run clinics in Australia.

Participants were randomized to mirtazapine 30 mg daily or matching placebo for 12 weeks. The primary end point was change in the number of days of methamphetamine use in the previous 28 days by week 12, assessed with the timeline follow-back method. Secondary outcomes included depression, insomnia, HIV risk behavior, quality of life, and the proportion of methamphetamine-negative oral fluid samples.

This framing makes the trial more clinically relevant. In stimulant use disorders, a meaningful reduction in use can still have important public health and functional benefits even if full abstinence is not achieved.

Why A Routine Clinical Practice Trial Matters

Many addiction trials show promise only under highly artificial research conditions. This study was designed to test something harder: whether mirtazapine still works when delivered through regular outpatient clinics to a broader patient population. That is why the trial has particular value — it asks a translational question that clinicians actually face.

The authors argue that their treatment effects are likely indicative of what can be expected in routine practice. In the absence of approved pharmacotherapies, a medication that is safe, inexpensive, generic, and can be prescribed as take-home treatment in outpatient care carries extra weight.

What The Trial Found

The main result was positive. The mean reduction in methamphetamine use days from baseline to week 12 was 7.0 days out of 28 in the mirtazapine group, compared with 4.8 days in the placebo group. The treatment difference was 2.2 fewer use days (95% CI -4.2 to -0.2, p = .02), corresponding to an 8% reduction in the risk of methamphetamine use on a given day.

Secondary outcomes were more mixed: there were no significant differences in methamphetamine-negative oral fluid samples, depression scores, insomnia, or HIV risk behavior in the overall sample. The reduction in use was not explained by improvements in mood or sleep, suggesting a more direct effect on addictive processes.

Safety was acceptable. There were no unexpected safety concerns, although drowsiness and weight gain were more common with mirtazapine, and discontinuation due to adverse events was higher than placebo.

What This Changes And What It Does Not Yet Change

This trial raises the level of confidence in mirtazapine. It is no longer just an intriguing idea from small early studies — it now has support from a multisite phase 3 randomized trial in routine care.

However, the effect size was modest, follow-up was only 12 weeks, and many practical questions remain (durability, subgroups, integration into broader care, comparative effectiveness). The study is clinically suggestive, but not yet field-changing.

Conclusion

This is not quite a breakthrough, at least not if that word implies a decisive shift in standard care. But it is more than a cautious early hint. The trial shows that mirtazapine can reduce methamphetamine use in adults with moderate to severe methamphetamine use disorder in routine outpatient practice, without unexpected safety problems. In a field with no approved medications, that is a consequential result.

Its real importance is that it moves mirtazapine from the category of plausible idea to the category of clinically credible option under active consideration. That is a meaningful step forward.

References

1. Manning, V., Arunogiri, S., Kelleher, M. J., Li, K. M., Khor, K. E., Goh, M. C. C., Cama, E., Berends, L., Lapworth, K., Sutherland, R., Kazemi, A., Quinn, B., Borowsky, B., Everett, N., Krivoy, A., Schonmann, Y., Sarid-Segal, O., Ezra, Y., Phan, Y., … McKetin, R. (2026). Mirtazapine for methamphetamine use disorder among adults in routine clinical practice: A phase 3 randomized clinical trial. JAMA Psychiatry. Advance online publication. Link to article

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