There are no studies showing its effects on healthy males, but it has been shown to drastically improve testosterone in infertile males (ref 77). It's also packed full of minerals, so is a great superfood nevertheless. I use the Sunfoods brand. Make sure you buy from a quality brand, as there are a lot of poor shilajit products out there, also some have been shown to be high in heavy metals. 
Hypogonadism (as well as age-related low testosterone) is diagnosed with blood tests that measure the level of testosterone in the body. The Endocrine Society recommends testing for suspected low T with a total testosterone test. It may be performed in the morning when testosterone levels tend to be highest in young men, although this isn't necessarily the case in older men. The test may be repeated on another day if the results show a low T level. (5)
The natural production of DHEA is also age-dependent. Prior to puberty, the body produces very little DHEA. Production of this prohormone peaks during your late 20’s or early 30’s. With age, DHEA production begins to decline. The adrenal glands also manufacture the stress hormone cortisol, which is in direct competition with DHEA for production because they use the same hormonal substrate known as pregnenolone. Chronic stress basically causes excessive cortisol levels and impairs DHEA production, which is why stress is another factor for low testosterone levels.
There are a lot of test booster blends out there. A lot of them are junk. I have tried to cover the most effective herbs above. As always, I recommend doing your own research and experiment to see if you notice an effect. If you would like one easy herbal solution I recommend starting with Mike Mahlers Aggressive Strength product purely because I have solid anecdotal evidence of its effectiveness. But again, supplements should be seen purely as that - a supplement to a healthy diet, plenty of sleep, hard training with adequate rest.
There is a negative correlation of testosterone levels with plasminogen activator inhibitor-1 (PAI-1) (Glueck et al 1993; Phillips 1993), which is a major prothrombotic factor and known to be associated with progression of atherosclerosis, as well as other prothrombotic factors fibrinogen, α2-antiplasmin and factor VII (Bonithon-Kopp et al 1988; Glueck et al 1993; Phillips 1993; De Pergola et al 1997). There is a positive correlation with tissue plasminogen activator (tPA) which is one of the major fibrinolytic agents (Glueck et al 1993). Interventional trials have shown a neutral effect of physiological testosterone replacement on the major clotting factors (Smith et al 2005) but supraphysiological androgen administration can produce a temporary mild pro-coagulant effect (Anderson et al 1995).
While researchers in Brisbane, Australia, found that while Testofen (“a standardized [fenugreek] extract and mineral formulation”) significantly improved the sexual arousal, orgasm, and the general quality of life of participants, it did not remarkably increase testosterone above normal levels. Participants who took Testofen were more satisfied with their energy, well-being, and muscle strength than those who took the placebo.
It seems like today it’s a badge of honor to train every day until exhaustion. The ethos is to push yourself harder and harder every day. If that’s your philosophy towards exercise, you might be sabotaging your testosterone levels (as well as your 20 Mile March). Studies have shown that overtraining can reduce testosterone levels significantly. Yes, it’s important to exercise hard, but it’s even more important to give your body rest so it can recuperate from the damage you inflicted upon it.
Men can experience a range of symptoms if testosterone decreases more than it should. Low testosterone, or low T, is diagnosed when levels fall below 300 nanograms per deciliter (ng/dL). A normal range is typically 300–1000 ng/dL, according to the U.S. Food and Drug Administration. A blood test called a serum testosterone test is used to determine your level of circulating testosterone.
Studies have demonstrated reduced testosterone levels in men with heart failure as well as other endocrine changes (Tappler and Katz 1979; Kontoleon et al 2003). Treatment of cardiac failure with chronic mechanical circulatory support normalizes many of these changes, including testosterone levels (Noirhomme et al 1999). More recently, two double-blind randomized controlled trials of testosterone treatment for men with low or low-normal serum testosterone levels and heart failure have shown improvements in exercise capacity and symptoms (Pugh et al 2004; Malkin et al 2006). The mechanism of these benefits is currently unclear, although a study of the acute effects of buccal testosterone given to men with chronic cardiac failure under invasive monitoring showed that testosterone increased cardiac index and reduced systemic vascular resistance (Pugh et al 2003). Testosterone may prove useful in the management of cardiac failure but further research is needed.
Fenugreek is often found in Indian, Turkish, and Persian cuisine. Multiple studies have found it to improve testosterone levels, and in particular, sexual performance. Scientists at Babu Banarasi Das University and King George’s Medical University in India have found that fenugreek improved testosterone levels. Testosterone levels increased for 90% of the volunteers, sperm morphology (the size and shape of sperm) improved for 14.6%, and more than 50% of volunteers experienced improvements in mental alertness, mood, and libido.
On review of the patient’s history, he was found to have undergone laboratory tests before starting to use the aforementioned testosterone booster product. All blood parameters (testosterone hormone and full chemical profile) before product intake were in the normal range. A physical examination that included blood pressure and pulse assessments showed nothing out of the ordinary, and the man appeared to be in good condition before product consumption. After that medical checkup, the athlete began to consume the product for 42 continuous days divided into 2 cycles (each cycle comprised 24 days). The daily dose was a single pack of Universal Nutrition Animal Stak (ingredients are listed in Table 1), following the exact direction of the manufacturing company hoping to get the best results.
Testosterone supplements are typically used by men who want to increase the level of the male hormone testosterone that controls functions such as sexual desire and muscle gain. There are several types of over-the-counter testosterone supplements available in nutritional supply stores. You should speak to your doctor before using any type of testosterone supplement since none of the effects advertised have been approved by the Food and Drug Administration. Additionally, there are prescription-based testosterone therapies that produce better results.
A: Testosterone is the male androgen, or sex hormone. It controls too many things to list here. While it does help regulate mood, sex drive, and metabolism, it does this by working in tandem with other hormones in your body. It's produced by the male testes and the adrenal glands. For more information, go to // Matt Curley, PharmD
Vitamin D3. Vitamin D3 actually isn’t a vitamin, it’s a hormone — a really important hormone that provides a whole host of health benefits. Our bodies can naturally make vitamin D from the sun, but recent studies have shown that many Westerners are vitamin D3 deprived because we’re spending less and less time outdoors. When we do decide to venture outside, we slather our bodies with sunscreen, which prevents the sun reaching our skin to kick-off vitamin D3 production. If you’re not getting enough sun, you may have a vitamin D3 deficiency, which may contribute to low T levels. If you think you need more vitamin D3, supplement it with a pill. Studies have shown that men who take this supplement see a boost in their testosterone levels. Because I have a darker complexion — which makes me prone to Vitamin D3 deficiency — I took 4,000 IU of vitamin D3 in the morning.
We reviewed the ingredient lists of our supplements and cut three that prescribed us an overdose of magnesium. While it’s possible to stay under the 350mg daily limit of supplemental magnesium by taking fewer pills than the manufacturer recommends, we were concerned that any manufacturer would advise you to exceed the recommended safety limit for magnesium intake by almost a third.
Try a protein deprivation diet. According to "Optimum Anabolics," the body produces more testosterone in response to heavy training when there is insufficient protein in the diet. Testosterone provides a hypertrophic, or muscle-building, backup system, allowing for muscle recovery when protein is not available. To follow this diet, take in only 30 grams of high-quality, fast-digesting protein (whey protein) immediately following your weight training. The rest of the days, your calories, split into five or six meals, should be divided between low-glycemic carbohydrates (oatmeal, whole grains and sweet potatoes) and healthy fats. After three weeks of this diet, switch back to a higher-protein diet (1 gram of protein per pound of body weight), adding one extra 20 to 30 gram serving of protein before bed.
The hormone also plays a role in sex drive, sperm production, fat distribution, red cell production, and maintenance of muscle strength and mass, according to the Mayo Clinic. For these reasons, testosterone is associated with overall health and well-being in men. One 2008 study published in the journal Frontiers of Hormone Research even linked testosterone to the prevention of osteoporosis in men.

Ashwagandha is shown to be effective at reducing cortisol which in turn helps with testosterone production. There are also numerous studies showing the effects on improving testosterone in infertile men (ref 80).  If you are using the Aggressive Strength product you don't need to supplement with ashwagandha as it's included in the test booster formula. Likewise if you're using Tian Chi (my daily herb drink).
During the month before my experiment, I was definitely sleep deprived. Some nights I was only getting 4 to 5 hours. Testosterone killer! During my experiment I tried to get 8 to 9 hours of sleep at night as consistently as possible. I had to go to bed earlier, but I was only cutting into time that I would have been using to mindlessly surf the net anyway.
There are numerous studies that show that Tribulus does not increase testosterone levels, and provides no assistance in increasing muscle mass or strength. I one of the two group of rugby players were put on the herb or a placebo. At the end of the experiment, there were zero changes in testosterone levels in the Tribulus group. Says a lot. [Source]
Testosterone is necessary for normal sperm development. It activates genes in Sertoli cells, which promote differentiation of spermatogonia. It regulates acute HPA (hypothalamic–pituitary–adrenal axis) response under dominance challenge.[22] Androgen including testosterone enhances muscle growth. Testosterone also regulates the population of thromboxane A2 receptors on megakaryocytes and platelets and hence platelet aggregation in humans.[23][24]

This is because your body is really good at self-regulating your hormone levels. So if you have normal testosterone levels, boosting above your natural base level may at best give you a few hours while your body makes, and then immediately processes out, the excess testosterone. This means you might experience higher than your average testosterone levels, but not by much, and only for a little while.

“Before taking Andro400, my husband weighed 290 lbs. He's a diabetic and his blood pressure was through the roof. I purchased Andro based on the reviews, and he's lost 60 - 70 lbs! ​It's enhanced him health-wise in a lot of aspects too. He used to be depressed because of his weight. The fact that he was losing weight like crazy gave him a lot of relief. He's not depressed now, he's really happy. He's more loving. And it's so exciting for me as a wife to see him happier -- it made me happier​! ​ So I'm really grateful. Andro400 gave him a lot of ​energy ​ too because of the testosterone boost.​ The 3 main things everybody's noticing are: no more​ depression, a lot more energy and ​the huge weight loss. He went from size 42 to 38, so it's like, oh my God it's WORKING!! Trust me, we've tried a lot of other things that didn't work. And that's why I'm so excited because it's actually, literally changing our lives!”
Testosterone makes a contribution to nitric oxide formation. Nitric oxide, released from penile nerves stimulates guanylate cyclase which catalyzes the transformation of guanosine-5-triphosphate into 3′,5′-cyclic, guanosine monophosphate (cyclic GMP). Gyclic GMP causes vasodilatation and hence erection formation (Morelli et al 2005). The breakdown of cyclic GMP to GMP is mediated by the enzyme, phosphodiesterase type-5, the inhibitors of which (eg, sildenafil citrate) enhance erection formation and maintanence (Carson and Lue 2005).

Now you know I prefer studies conducted on human participants instead of rodents, but often there is no choice.  A Japanese study on rats that you can read here: has demonstrated pretty convincingly that garlic supplementation significantly increases testosterone.  I wish there were more tests on humans but it turns out garlic isn’t patentable (sorry Monsanto) which means there isn’t enough financial interest to warrant human studies.  Maybe I’ll conduct one.  Any volunteers?
"Some say it's just a part of aging, but that's a misconception," says Jason Hedges, MD, PhD, a urologist at Oregon Health and Science University in Portland. A gradual decline in testosterone can't explain a near-total lack of interest in sex, for example. And for Hedges' patients who are in their 20s, 30s, and early 40s and having erectile problems, other health problems may be a bigger issue than aging.