Hello
Thanks for writing to us.

Anti depressants like mirtazapine are likely to cause decreased libido and erectile dysfunction on a long term use.

Drugs like viagra have been successfully used for the treatment of such disorders without any interactions.

You can easily combine them provided you have got yourself screened for all the risk factors that should be avoided while using viagra like , hypertension, angina, cardiac disorders, liver or renal dysfunction, etc.

You also need to inform your physician about your use of viagra for any further evaluation he might feel necessary.

I hope my answer and recommendations are adequate and helpful. Waiting for your further follow up queries if any.

Regards.

---