Please be careful. I had a hypertensive crisis a month ago, and I believe there is a strong chance it was because I took Nardil and Parnate together for a few days, though I can't say with 100% certainty.
TL;DR: I was on Nardil, then added Parnate for five days. My blood pressure spiked to 220/108 on Day 5, then crashed to 52/39 on Day 6, when I passed out twice. I made two trips to the ER in 24 hours. There are some caveats: foods or substances in my daily stack may have potentiated or possibly outright caused the situation, and I've had mild problems with autonomic regulation for most of my life too. Nonetheless, my suspicion is that the Nardil + Parnate combo was mostly or entirely to blame. Details below.
Sorry for the long-ass post, but if you're like I was, you're hungry for info from people who have actually tried the combo.
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WHAT HAPPENED: Parnate was very good for me, and Nardil has been nothing short of life-changing, yet I still wanted to get the best of both worlds by trying them together. I've experimented with easily 100+ pharmaceuticals, supplements, research chemicals, and drugs in my life, and have had some bad trips like everyone else, but nothing like this.
I've been on Nardil for six months (currently 60 mg/day), and I had been on Parnate for four months previously, so I had some Parnate left over. A month ago, I tried adding 10 mg/day Parnate to the Nardil. The combination worked well for three or four days: I had energy and focus from Parnate, while Nardil continued to keep anxiety in check.
However, at 3:30 pm on Day 5, I started feeling unusually "speedy" and anxious. By 4:00 pm, I could hear my heart thump and felt my head throb. At 4:50 pm, my blood pressure was 198/97 (I have a home sphygmomanometer); by 6:52 pm, it was 204/107. I was experiencing headache, nausea, akathisia, and an absolutely horrible pain in my abdomen that persisted for the next six hours (my doctor later said severe abdominal pain sometimes appears when blood pressure spikes).
I tried taking a regular dose of alprazolam (Xanax, a benzo) and a half dose of zolpidem (Ambien) to get my bp down, but they didn't help. I went to the ER, where my bp eventually hit 220/108 before coming down. They kept me under observation and sent me home around midnight.
Several hours later, around 3:00 am on Day 6, I woke up in the middle of the night to go to the bathroom. I felt woozy and uncoordinated as if very drunk, and fell over in the bathroom when trying to wash my hands. My wife heard the thump, saw me on the bathroom floor, and helped me back to bed, where I fell back asleep. At 8:30 am, I woke up and came downstairs feeling even more uncoordinated, then fell over onto the floor. At 9:00 am, I checked my bp, which was now 52/39.
The right thing to do then would have been to go back to the ER immediately, since bp as low as 52/39 is even more concerning than bp as high as 220/108. But I wasn't thinking straight; I was groggy and lethargic and just wanted everyone to leave me to lounge on the sofa. My systolic stayed in the 50s–70s and my diastolic in the 30s–50s all day, so I eventually went to the ER around 5:00 pm, where they gave me an IV. By 2:00 am, they discharged me. I've been fine ever since.
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CAVEATS
Caveat 1: I had recently added 4'-DMA-7,8-DHF to my daily stack as well, which otherwise consists of pretty innocuous stuff like zinc, magnesium, Vitamin B-6, Vitamin D, boron, fish oil, maca, tribulus terrestris, and the occasional racetam or sulbutiamine nootropic. For a little while after my bp incident, I thought the 4'-DMA-7,8-DHF was the culprit (it's a TrkB agonist but not very well studied, and I've found it to be wonderful for focus and slightly stimulating). However, I carefully reintroduced the 4'-DMA-7,8-DHF and have found it to be totally fine in combination with the Nardil. (It's still possible that it somehow potentiated the Nardil-Parnate combo.) The other stuff I'd taken for a long time together with the Nardil with no problems.
Caveat 2: In the 18 hours before the incident, I'd eaten a lot of one particular meat dish over three meals that surely had some tyramine in it, and ate almost nothing else (which is not my normal diet, fwiw!). So the hypertensive crisis could have been triggered by food or exacerbated by food. However, I've never experienced more than a barely noticeable reaction of any kind to any food or alcohol while on Parnate or Nardil. (This is not to say others should be as cavalier about the MAOI diet... please follow your doctor's instructions.)
Caveat 3: I have had mild problems with autonomic regulation for most of my life because of a brain injury, such as feeling woozy sometimes when doing strenuous physical activity. That may have contributed to my body's trouble regulating its own bp.
Caveat 4: As mentioned, I took a benzo and an Ambien around 7:00 pm on Day 5, which could have contributed to my grogginess overnight between Day 5 and Day 6. But I took them AFTER my bp spiked, so they didn't cause the spike; and according to my doctor, there's no way that in such ordinary doses, they were responsible for my bp crashing so low on Day 6.
IN CONCLUSION: Before trying them together, I'd read reports here on Reddit and elsewhere about people giving the Nardil+Parnate combo a shot. I'd also read the many warnings not to do so, but since the people issuing those warnings didn't seem to have any experience with the combo, I didn't take them seriously.
I do continue to think MAOIs are incredible meds and worth the risk, at least for me. However. I would be very careful about combining two irreversible ones like Nardil and Parnate.
If one were absolutely dead-set on doing so, I would guess that being on Parnate in a steady state and then adding Nardil might be safer than being on Nardil first and then adding Parnate (which is what I did). My logic is that one's catecholamine receptors have not downregulated as much in the latter case. But that's not an educated guess at all.
I'm not trying to rain on anyone's parade, and I realize my caveat conditions make my case far from a well-controlled experiment. I could be utterly wrong about Parnate + Nardil. I'm just suggesting you be careful out there.
Consider investing the $25 in a home sphygmomanometer before you start; it's probably a good thing for anyone on MAOIs to have anyway. And if you start spiking or crashing, get to a hospital.
P.S.: I was going to post photos of my bp measurements as evidence, but can't figure out how to post photos here... Happy to do it if someone can tell me how.