What Causes Severe Anxiety And Excessive Sleepiness While On Mirtazapine?

Hi, My partner is taking 45mg dose of mirtazapine, daily. He is suffering with heightened anxiety, including social anxiety, and sleeps too much (when he finally gets to sleep). It s effecting our relationship as he wants to remain alone the majority of the time and prefers to have some phone conversation each day, but be by himself. I am incredibly patient and am giving him his space, which he knows and appreciates, but he is keen to try something that can help him relax around friends and family as refraining from seeing people is having a major impact on his recovery. Can he take kalms whilst on mirtazapine?