In recent years, more cases of manic switches on Mirtazapine have been reported. In this report, we discuss a case of manic switch in a gentleman who was treated as unipolar depression. A 66-year-old man presented to psychiatry 8 months following a nephrectomy for symptoms of depression. Treatment with Sertraline 50mg daily was initiated and titrated to 150mg, along with Zolpidem and Clonazepam to aid his sleep. Despite these medications he never achieved remission and continued to have persistent anxiety and insomnia. Due to suboptimal control, treatment was changed to Mirtazapine 15mg daily. At day 20 he showed symptoms of mania which included talkativeness, increased goal directed activities, reduced need for sleep and socially disinhibited behavior. Mirtazapine was discontinued, and treatment was changed to Sodium Valproate, optimized to 1000mg daily, augmented with Quetiapine 150mg daily. Remission was achieved after 4 months and he has remained asymptomatic for 2 months. This was his first episode of mania, and a diagnosis of Bipolar I disorder was made. In conclusion, antidepressant induced manic switches are common, they are relatively under-appreciated and under-reported, especially with the use of sleep-promoting antidepressants. All antidepressants should be considered to be a potential mediator of a switch in view of its pharmacological properties.