Hi there, thanks for asking. Venlafaxine
does not weaken the immune system. It may have some side effects which are mostly manageable with lowering the dose or adding another medication. It is a good medication for treating depression
as well. If she feels that she is not comfortable with this medication, she can ask her doctor to give her another medication. Post pregnancy
depression is a serious disorder and should be treated completely. If the medication is discontinued by doctor, she will remain well after. Best wishes.