http://www.ncbi.nlm.nih.gov/pubmed/20833158

"Taken collectively, these results indicate that (a) mitochondria are target organelles for harmine, which elicits cytotoxicity through mitochondrial failure related to the induction of the MPT, mitochondrial depolarization, and inhibition of ATP synthesis; and (b) the toxic effects of harmine are greater than those of either its metabolite harmol or its analogue harmaline, suggesting that the onset of harmine-induced cytotoxicity may depend on the initial and/or residual concentrations of harmine rather than on those of its metabolites."

Thoughts?

Makes sense, lots of things are toxic when you put them on cells in-vitro.

However several long term studies show that harmine is quite safe and has even been looked at by pharm companies as an over the counter antidepressant, the reason this was not done was because they could not patent harmine containing plant species.

if you look you can find similar articles about many things, like caffeine

the metabolism of such alkaloids in-vivo is often entirely distinct from their metabolism in-vitro and such articles are meaningless when it comes to use of the molecule for our purposes

This study gives us an idea of what harmine can do in isolated liver cells from a rat, that doesn't necessarily correlate with what happens in a healthy human body. I've pulled up similarly concerning papers about the in vitro toxicity of harman and norharman (found in Tribulus terrestris and some other plants). And yet, the plants that contain these alkaloids haven't been convincingly shown to have a toxic effect in vivo. Take these studies with a grain of salt, I say.

Since the toxicity described involves generation of oxygen radicals and reduction in glutathione levels (this is common to many different toxins), if you were really concerned you could make sure to include lots of antioxidants in your diet, and supplement with herbs like milk thistle that directly support levels of glutathione in the liver.