First off I'll start out by saying yohimbine is a mild MAO inhibitor. but MAO inhibitors are a broad category, they certainly do not all work in the same way or have the same effects.
I disagree that yohimbine is not selective at all. There is a study from 1988 that disagrees with this. This study also goes on to state that when rats are given 200mg/kg of tyrosine in addition to 10mg/kg of Yohimbine that and I quote "Moreoever, the administration of 200 mg/kg of tyrosine failed to augment the increases in brain MHPG and DGPH produced by PB. Tyrosine did slightly enhance the increase in DHPG due to YOH treatment. This effect is presumable a result of YOH activating these neurones by blocking presynaptic autoreceptors and thus making the rate of NE turnover dependent on tyrosine availability(wurtman et al., 1981). How ever no such effect was observed for th YOH-induced increase in MHPG. The reason for this is unknown, but may relate to NE being preferentially converted to DHPG when metabolized intraneuronally and to mHPG when metabolized extraneuronally. Finally, the large elevation in MHPG due to YOH may be due only partly a2-adrenoceptor blockade. YOH is structurally similiar to reserpine and has been postulated to cause a reserpine-like release of stored NE. The acute biochemical effects of a single injection of reserpine caused both increases in braing MHPG and decreases in NE similar to those caused by YOH(Bareggi et al., 1979). Thus, 2 hr after a dose of 1.25 mg/kg of resperine, MHPG was increased 72% and NE was reduced 43%(bareggi et al., 1979). On the other hand since YOH did not deplete brain DA, if YOH has a reserpine like action, it must be selective for NE neurons."
here is another quote from this study's abstract "Tyrosine failed to enhance the effect of either YOH or PB except for somewhat augmenting the increase in DHPG induced by YOH"
Essentially what I am saying here is that all MAOi's dont act the same... In this study tyrosine has basically an insignificant effect on the brain when combined with yohimbine. Now if some one wants to argue the effectiveness of yohimbine that is a different argument that I think has been disputed here a thousand times. I personally like the results I have gotten from yohimbine but it is always up to the consumer to read up on a substance and gauge their bodies tolerence to it. Also i think it is important to understand that we have dosed leviathan very modertly with tyrosine. When this product was formulated we researched tyrosine and yohimbine extensively. We absolutely were interested making leviathan a safe but effective product. Here is the link to the abstract from pub med:
http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?cmd=Retrieve&db=PubMed&list_uids=3251333&dopt=Abstract
Oh I also agree completely with Sldgehmr on his assessment off yohimbe bark.. Never use a product that uses yohimbe bark.. it is a dirty herb(yohimbine is only 1 of the 32 active alkoloid present in yohimbe) If you use a product make sure it is a straight yohimbine HCl product.. not an yohimbe bark standerized to a % yohimbine.
Yohimbe and its Alkaloids Should be Banned: An Unpopular, Quick Think Piece