Mirtazapine induced nightmares in an adult male

A 21-year-old medical student was prescribed mirtazapine 15 mg once daily at bed time for his depressive symptoms. After taking the drug for approximately 2 weeks, he again presented to the psychiatry outpatient department with a history of severe nightmares almost every night.

During history taking, he could recollect few of the horrifying experiences that he dreamt of. In one of the dreams he saw an unknown person trying to stab him with a knife. In another, he saw himself tied up to a pole over the bridge and gun shots hitting him from the sides. In the third, he visualized his girlfriend dead under a collapsed building. He also reported dreaming about his own cremation proceedings going on at a barren place, while he was still alive.

Each time he woke up with confusion, palpitations, sweating and fear. In addition, he complained of malaise, confusion and increased sedation during day time, while on therapy. The drug was consequently stopped and, not surprisingly, the nightmares disappeared completely within a couple of days. Thereafter, he was put on fluoxetine and no such episodes were reported. On careful evaluation of past history, it was found that the patient had shown poor compliance to mirtazapine a few years back and had experienced similar nightmares.

There was no history of concomitant use of other medications (including herbal medicines) or alcohol intake. The temporal relationship between the initiation of treatment with mirtazapine and onset of nightmares and their disappearance with discontinuation of the drug, and also their occurrence during a previous episode of mirtazapine treatment suggest a causal aetiology and puts this extremely rare adverse drug reaction (ADR) in a ‘highly probable’ category according to the Naranjo Algorithm with a score of 9 [1].

Mirtazapine is a tetracyclic noradrenergic and specific serotonergic antidepressant drug and is widely used in the treatment of depression. The most common adverse effects reported from mirtazapine, in a prescription event monitoring study done in more than 13 000 patients in England, include drowsiness/sedation and malaise/lassitude [2]. Sleep disorders are extremely rare adverse events with mirtazapine and only one case of mirtazapine-induced nightmares has been cited in literature [3]. An episode like the one reported here is rare and definitely merits a mention.

Since most antidepressants suppress rapid eye movement sleep [4], they are known to cause insomnia rather than nightmares. Mirtazapine, on the other hand, has been documented to show sleep-promoting action by increasing total sleep time, sleep efficiency and slow wave sleep [5]. Also, when given in the dosage of 30 mg 2 h before bedtime in healthy volunteers, it showed shortening of sleep onset and decreased bedtime waking and dozing [6]. This is probably one of the reasons for a causal association between mirtazapine and nightmares. A 2-year prescription monitoring undertaken by the Australian ADR Advisory Committee has shown that nightmares accounted for only 14 spontaneously reported events from almost 500 000 funded prescriptions [7].

On the other hand, in an interesting report, Lewis shared his experience, where addition of mirtazapine in the treatment regimen of post-traumatic stress disorder successfully reduced the frequency and intensity of nightmares in more than 200 refugees [8]. This makes the situation even more confounding as regards the appropriateness of its use in nightmares.

Nevertheless, prescribers, especially psychiatrists, should be aware of the fact that there are many more drugs known to cause nightmares [9]. These cases may be wrongly diagnosed as some psychiatric illness. Taking a proper history of drug use thus becomes an important tool in clinical practice.

Competing interests

None declared.