@SDSue - As has been mentioned above, Mirtazapine is an ADRA2A antagonist. Repressing ADRA2A can increase norepinephrine release or levels, which can raise blood pressure and/or pulse pressure. This can help with hypotension.
A list of drugs which have this action are at http://en.wikipedia.org/wiki/Alpha-2A_adrenergic_receptor - Some are much more specific in their actions than others. Yohimbine is the most specific, since it has a strong action at ADRA2A, 2B, and 2C and nothing else. Mirtazapine, on the other hand, has a stronger action on a Histamine receptor, and strong actions on seretonin receptors.
I don't get side effects from Yohimbe, but I take a pretty small dose. They usually come in 400mg capsules, and I split those into 4 100mg capsules and take it twice per day. If I take it past 2pm or so, it can be too over-stimulating to sleep, even with the small dose. I also test low for serum norepinephrine, which might be an indication for whether or not it's likely to be helpful.
If a low dose of yohimbe isn't helpful, and/or norepinephrine isn't low, there might be some other effect of the mirtazapine which was helpful, such as acting as an H1 antagonist.
A list of drugs which have this action are at http://en.wikipedia.org/wiki/Alpha-2A_adrenergic_receptor - Some are much more specific in their actions than others. Yohimbine is the most specific, since it has a strong action at ADRA2A, 2B, and 2C and nothing else. Mirtazapine, on the other hand, has a stronger action on a Histamine receptor, and strong actions on seretonin receptors.
I don't get side effects from Yohimbe, but I take a pretty small dose. They usually come in 400mg capsules, and I split those into 4 100mg capsules and take it twice per day. If I take it past 2pm or so, it can be too over-stimulating to sleep, even with the small dose. I also test low for serum norepinephrine, which might be an indication for whether or not it's likely to be helpful.
If a low dose of yohimbe isn't helpful, and/or norepinephrine isn't low, there might be some other effect of the mirtazapine which was helpful, such as acting as an H1 antagonist.