Assuming you mean Mirtazapine - brand name of Zispin SolTab
I found the following potential side effects listed for it. Whilst almost all of us on here really have no medical knowledge, those side effects I've highlighted in red might be an issue for the medical people.
Feeling sleepy, dizzy, or tired - **If this happens, do not drive and do not use tools or machines. - Do not drink alcohol ... Headache ... Dry mouth ... Increased appetite and weight ... Common mirtazapine side-effects - these affect less than 1 in 10 people who take this medicine ... Feeling sick (nausea), diarrhoea ... Disturbed sleep, feeling anxious, rash, swollen feet and ankles, aches and pains, feeling shaky
**Emphasis on the "if"
Prior to their reply, no harm in asking your GP if there is an alternative with less side effects.