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Better than asparagus ;-)

I have to admit, it has been a while since I've written about "natural testosterone boosters". In the last article that was remotely related to this topic, I even wrote that they are useless for 90% of the male population, because even if they boost your testosterone levels by 10-20% this is very unlikely to have the muscle building and fat burning effects that are marketed on the packages of and in the ads for respective products. Why? Well, even with real gear it takes more than just a 10% boost within the normal range before you see results (learn more | specifically Figure 2 where green is the large "normal" range).

So why do I even bother about yet another rodent study dealing with the ability of a more or less exotic flowering plant found in Benin, Cameroon, Democratic Republic of the Congo, Ivory Coast, Gabon, Ghana, Liberia, Nigeria, Senegal and Sierra Leone and its ability to boost testosterone levels?
Well, considering the fact that erectile dysfunction is a widespread disorder affecting approximately 52% of men between the ages of 40–70 years (Vitezic. 2002), some of you may actually benefit from a natural testosterone booster, specifically if the latter affects not just the mere level of testosterone, but also your libido, sperm count and erectile function. And that's three things Garcinia Cola can do.

Well, at least what scientists from the Walter Sisulu Universitty found when they used administered a  Garcinia Cola (bitter cola) extract produced by extracting G. cola seeds using 70% ethanol as solvent at dosages of 200 and 400 mg/kg, i.e. 32mg/kg or 64mg/kg for human beings, based on evidence from a previous study, which demonstrated sexual behaviour improving capacity after 28 days of treatment (Ralebona. 2012). To make sure that we couldn't get away with much less the scientists added a third, lower dose of 100 mg/kg (16mg/kg for humans | learn how this is calculated).

Figure 1: The Garcinia cola extract improved the number and success rate of ejaculations (Sewani-Rusike. 2015).

The extract was administered for 56 days in total with intermittent "mounting tests" to assess the effects on the rodents sexual performance after 25 and 50 days and a detailed assessment of organ weights, sperm count, reproductive hormone levels and testicular histology when the study and *sigh* the poor rats were "terminated."

Figure 2: The extracts improved the mount latency, the intromission latency, the number of mounts and intromissions early, i.e. after 28 days and late, i.e. after 50 days in the study (Sewani-Rusike. 2015)

That was particularly unlucky for the rodents in the control group that had significantly "less fun" on the two test days. Most intriguingly, the best sexual performance as measured by the lowest time to hop onto and into the dame and the highest number of mounts and frequencies was actually observed with the lowest dosage of Garcinia Cola, i.e. 100mg/kg or 16mg/kg for a human being).
The increase in sexual performance went hand in hand with increases in testes weigh at constant prostate and epididymis and seminal vesicle weights (good news), and ~50% increases in sperm count at non-significantly improved sperm motility and viability rates (see Table 1).

Table 1: The effect of 56-day treatment with Garcinia Cola extract on reproductive organ weights (% body weight) and sperm counts (Sewani-Rusike. 2015)

All these beneficial changes, as well as the significant increase in serum testosterone (see Figure 3), at identical LH and FSH levels and the absence of body, heart, liver, kidney and spleen levels gains or pathological changes to any of these organs or the testes, clearly suggest that Garcinia Cola seed extracts derive their potent aphrodisiac activity mostly from improvements in testicular function.
References:

From a physiological perspective NO is not primarily there to make you look vascular and pumped, boys.

If you've read the headline and are asking yourselves "Why on earth would I even want to spend money on cosmetic pump?", you probably need a reminder of the multiple important functions nitric oxide (NO) serves in your body: (1) With their ability to relax the musculature of your blood vessels to increase the blood flow through your veins, normal NO levels are required to guarantee optimal blood flow to every body part; (2) since this includes your sexual organs, normal NO levels are also a prerequisite for normal / optimal sexual function; (3) having enough NO is also required to keep your immune defenses up, because the white blood cells need it in their fight against intruders; and if heart disease, sexual dysfunction and immune health are all things you don't care about (4) you may be interested to hear that your brain and metabolic health critically depend on normal NO levels, as well.
Now that you've got the primer on "nitric oxide beyond the pump" you may be happy to hear that a very common NO supplement, i.e. citrulline, actually delivers. But there's more: In a very recent study, scientists from the Baylor University demonstrated for KYOWA HAKKO BIO CO (so this is sponsored research) that a combined treatment with citrulline and glutathione leads to significant increases in the levels of cGMP, nitrite, and NOx (nitric oxide metabolite) in cells, rodents and humans.

Figure 1: Overview of the design of the "human part" of the study (McKinley-Barnard. 2015).

In the latter part of the study (the human part), the researchers had sixty six participants randomly assigned (in a double-blind fashion) to one of four groups (n = 15 per group) involving 7 days of the oral ingestion of four capsules containing a total daily dose of either: cellulose placebo (2.52 g/day), L-citrulline (2 g/day), GSH (1 g/day), or L-citrulline (2 g/day) + GSH (200 mg/day). Supplementation compliance was monitored by participants returning empty containers of their supplement on day 7, and also by completing a supplement compliance questionnaire.
Each participant ingested all four capsules containing their respective daily supplement dose each evening for six consecutive days until at Visit 3 (Day 7), participants were provided the final daily dose of their respective supplement ingested one hour prior to performing a previously familiarized biceps training program consisting of  3 sets of 15 repetitions with as much weight as they could lift per set (typically 70–75 % of 1RM | 10s rest between sets, only) on a selectorized weight machine (Body Master, Rayne, LA).

Figure 2: Nitrate concentration and change in plasma NOx in rodents (NO metabolites | McKinley-Barnard. 2015).

Figure 2, which depicts data from the rodent study, already suggests that only citrulline or citrulline and glutathione would trigger significant increases in NO production in the 20-22 year-old healthy, well-trained (at least three resistance training sessions per week) participants, while GSH alone would trigger only a minor increases of the nitric oxide levels.

Figure 3: Changes in NO metabolites (NOx) and cGMP levels (McKinley-Barnard. 2015) in the human study.

The data in Figure 3 (left) which tells you that the increase in stable NO metabolites (NOx) in the blood of the subjects in the citrulline + GSH group was the highest. What may surprise you, though, is that the increase in nitric oxide that is obviously partly mediated by an increase in c-GMP (Figure 3, right) levels was not only maintained after the workout, the levels even kept increasing.
This is in contrast to your regular "pump" formula (using only citrulline), where the levels drop back to baseline ( and potentially even lower - after all only 30 min were monitored) after the workout.

Why is that important? Well, if you look back at the "nitric oxide beyond the pump" list from the introductory paragraph, you will notice that almost all of these "beyond the pump" effects are health-relevant during, but also and even more so after the workout.
References:

• Ghigo, D., et al. "Correlation between nitric oxide synthase activity and reduced glutathione level in human and murine endothelial cells." Amino acids 10.3 (1996): 277-281.
• Hofmann, Heinrich, and Harald HHW Schmidt. "Thiol dependence of nitric oxide synthase." Biochemistry 34.41 (1995): 13443-13452. 
• McKinley-Barnard, Sarah, et al. "Combined L-citrulline and glutathione supplementation increases the concentration of markers indicative of nitric oxide synthesis." Journal of the International Society of Sports Nutrition 12.1 (2015): 27.