Mirtazapine for PTSD-Related Nightmares
With prazosin's evidence base weakened by a large negative trial, mirtazapine offers a genuinely different mechanism for trauma-related nightmares — built on a smaller evidence base of its own, and carrying a side-effect profile that cuts both ways for this patient.
R.L. is a 52-year-old man, a retired corrections officer, whose PTSD-related nightmares have persisted despite a six-month trial of prazosin titrated to 10 mg at bedtime, discontinued three weeks ago after he and his prescriber, weighing the negative PACT trial data directly against his own lack of response, agreed it was not worth continuing further titration. He lives with his adult son since a recent divorce, has type 2 diabetes managed with metformin, and has struggled with poor appetite and gradual weight loss over the past year that both he and his son have noticed independently.
His prescriber raises mirtazapine as an alternative, a genuinely different mechanism from prazosin's alpha-1 blockade: mirtazapine's sedating, sleep-promoting effect comes primarily from histamine H1 and serotonin 5-HT2A/5-HT2C antagonism, and it carries a smaller, less rigorously tested evidence base in PTSD than prazosin ever had, built mostly on smaller augmentation trials rather than a single large, well-powered study. What makes it a genuinely interesting fit for R.L. specifically, rather than simply the next drug on a list, is his poor appetite and weight loss — mirtazapine's well-known appetite-stimulating and weight-gain side effect, generally listed as a drawback in most patients, could plausibly help him on both fronts at once. The same side effect could just as easily be a liability in a different patient with obesity or poorly controlled diabetes, which is exactly why this isn't a case of one drug being simply "the next option" once prazosin fails, but a choice that depends specifically on who is sitting in front of you.
At the follow-up visit
Mirtazapine is a genuinely different mechanism, not just a fallback drug, and for R.L. specifically the appetite-stimulating side effect other patients are warned about could be a real secondary benefit given his weight loss over the past year. I'd frame it to him honestly as a smaller evidence base than prazosin's original reputation, not as a proven replacement.
Worth being precise about how much smaller that evidence base is — the mirtazapine-for-PTSD literature is mostly smaller augmentation trials, not a single trial of PACT's scale in either direction. That doesn't mean it won't work for him; it means we genuinely don't know as much about it, which is a different situation from prazosin's reversal, where a strong original signal was later contradicted by a larger trial.
Given his diabetes, I want to flag mirtazapine's weight-gain effect as something to actually monitor rather than assume is purely beneficial — some weight recovery is genuinely welcome here, but I'd like a follow-up in six weeks checking both his glucose control and whether the weight change is trending toward a healthy range rather than overshooting it.
Mirtazapine started at 15 mg at bedtime, with a six-week follow-up specifically monitoring glucose control and weight trend given his diabetes.
Agreed clearly: mirtazapine was chosen because its particular side-effect profile fit R.L. specifically, not because it is an established replacement for prazosin in general — the team was explicit that this same choice could look wrong for a different patient with obesity or poorly controlled diabetes.