Cellucor P6 Ultimate isn't even the best testosterone booster in the Cellucor P6 lineup, never mind on the market at it's price range.
Now, that's not to say it's a completey terrible supplement, there's definitely some things in here that will improve workouts and could lead to an increase in lean muscle mass, it's just not being honest when it markets itself as a testosterone booster. Most of the ingredients are more geared towards working out than doing much about test levels.
Cellucor P6 ultimate does have some tongkat ali, 100mg, which is on the lower end of doing and would take longer to have any effect, although it's not one of the most well backed test boosting ingredients despite it's popularity. And there is DIM, which has some evidence to support it blocking estrogen, although there is a lot of evidence to suggest it shouldn't be taken for a long time.
Beyond that there's some vitamin D, and the rest of the ingredients are either shown to improve workouts or only backed in animal studies in terms of testosterone production.
It does also miss out on some core vitamins that we expect to see in testosterone supplements like vitamin D, Ashwagandha, Fenugreek and Ginseng. Many of which are in other Cellucor P6 products, which leads us to wonder why exactly they were left out of the ranges premium option.
All in all if you're just looking for a workout boost it could be fine, but at this price range there are far better options for both work out aids and testosterone boosters.
Cellucor P6 Ultimate is a dietary supplement marketed as a testosterone booster. It is designed to support natural testosterone production in the body and promote muscle growth, strength, and overall performance. Unfortunately almost none of the ingredients in Cellucor P6 ultimate raise testosterone levels the way it claims and it should not be mixed up with their far better original supplement Cellucor P6 which contains a blend of ingredients such as Tribulus Terrestris, Fenugreek, and Saw Palmetto, which are commonly associated with potential benefits for testosterone levels.
Not really, it has a couple of ingredients that could be and should be beneficial for your workout routine, so if you're looking to improve that and only that, then in a manner of speaking it could work. But there are much better options, when it comes down to how well Cellucor P6 works as a testosterone booster however, we would say not particularly well. It does contain a couple of ingredients known to boost testosterone, but one Tongkat Ali, only works after you've been taking it for some time (at the dosage in Cellucor) and the other DIM, should only be taken for a short amount of time, which sort of puts everything into a bit of a bind,
So first up, we should say that there's a lot of positive reviews for cellucor p6 ultimate as a workout supplement, it doesn't really do much at all for any of the other reasons people take test boosters for. Almost none of the positive reviews mention any improvements to mood or "ahem" drive "ahem".
There are definitely a large portion of the Amazon verified reviews of Cellucor P6 which have been insentivised, this isn't really a new phenomenon, but after normalizing for this the average was a little under 4*.
As for negative cellucor P6 reviews these were particularly bad, not only did we get the usual "it didn't work for me" type complaints, but we had some people complaining of severe stomach damage for taking it over a prolongued period of time.
Also as you'd expect considering there's little in here to boost testosterone, nobody mentioned that. Ultimately this is a work out supplement and shouldn't really be marketed as a testosterone booster.
DIM (Diindolylmethane) 100mg: Some studies suggest that DIM may support healthy estrogen metabolism, which could indirectly impact testosterone levels. However, more research is needed to establish a direct link. There are also some issues with taking DIM over long periods of time, with some studies suggesting that this can in fact lower testosterone levels. 
Longfolia (Eurycoma longifolia) 100mg: Also known as Tongkat Ali, Longfolia has been traditionally used to enhance male fertility and libido. While some animal studies have shown a positive effect on testosterone levels, human studies are limited. However, even if we do assume it works, 100mg is on the lower dosing end, which would mean it would take about 12 weeks to have any effect on testosterone levels according to the existing studes., which isn't ideal in a supplement you can only take for a few months without feeling ill if the customer complaints (and what we know about DIM) are to be taken into consideration. 
Ancient Peat 150mg: Ancient peat contains various minerals and trace elements. While it may support overall health, there is insufficient evidence to suggest a direct impact on testosterone levels. 
Velvet Bean (Mucuna pruriens) 416mg: Velvet bean contains L-dopa, a precursor to dopamine, which plays a role in testosterone production. Some studies have suggested a positive effect on testosterone levels, but more research is needed to confirm these findings. Almost all studies currently are on animals and there isn't really anything to substantiate that this will work in humans. 
Shilajit 500mg: Shilajit is a mineral-rich substance that is believed to have various health benefits. While some studies have shown a positive impact on testosterone levels, more research is needed to establish its effectiveness. This is probably best for mental acuity and potentially has some mood boosting effects, but it isn't as effective as we'd expect something like Ashwagandha to be for most people. And that would take up a similar amount of capsule space. 
L-Lysine HCl and L-Arginine 1200mg: These amino acids are involved in protein synthesis and have a role in hormone production. However, their direct impact on testosterone levels is not well-established, and to be quite frank almost none existant, there is some evidence to suggest that they can help with muscle growth however. 
Vitamin D 125mch: Vitamin D deficiency has been linked to low testosterone levels. Supplementing with vitamin D may help raise testosterone levels in individuals with deficiencies, but it may not have the same effect in those with normal levels, it has however been shown to improve athletic performance when supplementing beyond normal levels, which considering a lot of men buy testosterone boosters for muscle growth, this makes it a good inclusion. 
Vitamin B6 1mg: Vitamin B6 is involved in testosterone synthesis. However, there is limited evidence to suggest that supplementing with vitamin B6 alone can significantly raise testosterone levels unless a person is deficient in multiple b vitamins which is relatively rare. It's a small inclusion in the capsule however and can improve energy levels reducing the symptoms of low test, but again this is a standard ingredient in most, much better testosterone boosters. 
Cellucor misses zinc, which is actually the most effective testosterone vitamin when we account for the fact that even a minor deficiency can tank testosterone levels. And it's particularly prevelant in the USA with some studies suggesting almost 30% of American men over 50 could have a sub clinical deficiency. 
1 - https://pubmed.ncbi.nlm.nih.gov/26926141/
2 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC9415500/
3 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4950767/
4 - https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3942911/
5 - https://pubmed.ncbi.nlm.nih.gov/26395129/
6 - https://pubmed.ncbi.nlm.nih.gov/6257011/
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8 - https://pubmed.ncbi.nlm.nih.gov/6727359/
9 - https://pubmed.ncbi.nlm.nih.gov/8875519/