https://www.medicalnewstoday.com/articles/mirtazapine-oral-tablet#important-warnings

FDA warning: Suicide risk: “This drug has a black box warning. This is the most serious warning from the Food and Drug Administration (FDA). A black box warning alerts doctors and patients about drug effects that may be dangerous.
Mirtazapine may cause an increase in suicidal thoughts or actions. This risk is higher in children, teenagers, and young adults. It’s also higher within the first few months of treatment and during dosage changes. You and your family members, caregivers, and doctor should watch for any new or sudden changes in your mood, behaviours, thoughts, or feelings. Call your doctor right away if you notice any of these changes”.