The truth about testosterone boosters (what actually works)

The testosterone supplement industry is enormous. The marketing is slick. The studies cited in the marketing are usually real but selectively cherry-picked.

What follows is what the evidence actually says about the most popular testosterone supplements, and the second story the industry hopes you skip past, which is more important than any pill in the category.

Why testosterone matters

Low testosterone in men, clinical hypogonadism, has genuine health implications: body composition, energy, mood, libido, bone density, and cardiovascular health. The question is not whether testosterone matters. It does.

The questions worth asking are:

1. Do these supplements actually raise testosterone in healthy men?
2. If so, by how much, and is the effect clinically meaningful?
3. How does the supplement effect compare to lifestyle factors?

The answers vary substantially by supplement, and most of them are underwhelming.

Tongkat ali (Eurycoma longifolia)

Tongkat ali has the most plausible evidence base after ashwagandha.

Several studies have shown modest testosterone increases. Roughly 15-37% in some trials. The most meaningful effects appeared in men who were stressed or who had genuinely low testosterone to start with. The proposed mechanism involves suppression of sex hormone binding globulin (SHBG), and possibly cortisol reduction.

Important caveats:

• Most studies are small (n<50) and short-term (4-12 weeks).
• A non-trivial fraction have financial conflicts of interest.
• The effect on free testosterone (the biologically active form) is less clear than the effect on total testosterone.

I’m not dismissing tongkat ali. There’s real signal here. But the marketing far outpaces the evidence, and the magnitude of benefit in a healthy non-stressed man with normal testosterone is probably smaller than is often claimed.

Fadogia agrestis

A different story. The human evidence is essentially non-existent as of 2024-2025. Almost all the data is in rodents.

The rodent studies do show testosterone-increasing effects. They also show safety concerns, including potential hepatotoxicity, that have not been adequately studied in humans.

This is a supplement being sold aggressively on the back of animal-only data. I tell patients to wait for proper human trials. This category warrants real caution.

Ashwagandha (Withania somnifera)

Probably the best-evidenced of the commonly marketed testosterone supplements, with an important caveat.

A 2019 randomised, double-blind, placebo-controlled crossover trial in 50 overweight men aged 40-70 found that 8 weeks of standardised ashwagandha extract was associated with a 14.7% greater increase in testosterone and 18% greater increase in DHEA-S versus placebo (p<0.05 for both).¹

The caveat: ashwagandha doesn’t directly stimulate the testes to make more testosterone. The mechanism appears to be cortisol reduction. Lower cortisol allows testosterone to express more fully. Effects are most reliable in chronically stressed men.

If you’re going to try one supplement in this category, ashwagandha is the most defensible choice. But understand what you’re actually buying. A stress-reducing herb that indirectly supports testosterone, not a direct production booster.

D-aspartic acid

Initial studies looked promising. Follow-up randomised trials in young healthy men doing resistance training showed no benefit and in some cases decreases in testosterone.

The current evidence does not support D-aspartic acid as a reliable testosterone booster in healthy men. The picture is unclear at best. Skip it.

Zinc and vitamin D

These aren’t testosterone boosters per se. They’re deficiency correctors.

If you’re zinc-deficient or vitamin-D-deficient, your testosterone may be lower than it should be, and correcting the deficiency can normalise it. But supplementing above repletion in someone with normal levels doesn’t add benefit.

Get a level checked. If you’re low, replete. If you’re not, save your money. The “more is better” approach doesn’t apply here.

What actually matters: the four variables

This is the part the supplement industry hopes you skip.

1. Sleep

The single largest modifiable testosterone variable. One week of restricted sleep (5 hours per night) drops testosterone by roughly 10-15% in young healthy men. The mechanism is the disruption of the nocturnal testosterone pulse, which depends on REM sleep architecture.

If you’re chronically sleeping 5-6 hours and considering a £40/month testosterone supplement, fix the sleep first. The biological effect will be larger than anything you can buy.

2. Resistance training

Compound movements with heavy load. Squats, deadlifts, presses, rows. Acute spikes in testosterone post-workout, plus long-term support of basal levels, plus all the body-composition and metabolic benefits. Two to three sessions per week of progressive resistance training is the highest-leverage intervention available.

3. Body composition

Excess body fat, particularly visceral fat, increases the activity of aromatase, the enzyme that converts testosterone to oestrogen. It also lowers free testosterone through SHBG dynamics. Reducing visceral fat reliably raises testosterone in men with elevated body fat.

This is part of why ashwagandha and tongkat ali show their largest effects in stressed or overweight men. There’s more room for the underlying biology to recover when those variables are addressed.

4. Chronic stress

Cortisol, the chronic-stress hormone, suppresses the HPG axis (the hormonal pathway that drives testosterone production). Chronic elevated cortisol means chronically suppressed testosterone, and no supplement reliably overrides this if the stress isn’t addressed.

This is also why ashwagandha works. It lowers cortisol, removing the suppressive signal.

When testosterone replacement therapy is appropriate

TRT is appropriate medical treatment for genuine hypogonadism:

• Repeated morning blood tests confirming clinically low testosterone (typically below 300 ng/dL or 10.4 nmol/L).
• Corresponding clinical symptoms (low libido, persistent fatigue, mood changes, body composition shifts, reduced morning erections).
• After lifestyle optimisation has been adequately attempted.

Done correctly, TRT has established benefits for body composition, mood, and libido in genuinely hypogonadal men.

It is not a longevity intervention or a performance enhancer for men with normal testosterone. The cardiovascular safety profile is nuanced and depends on dose, monitoring, and patient factors. This is a conversation for your own doctor, not for online clinics.

The bottom line

The testosterone supplement market is built on the gap between what the marketing promises and what the evidence supports.

The most defensible options have modest effects. Ashwagandha does something, mostly through cortisol. Tongkat ali probably does something, mostly in stressed or hypogonadal men. Most of the rest have weak or absent human evidence.

The four lifestyle variables. sleep, resistance training, body composition, stress. Produce larger effects than any supplement in this category. Get those right first. The supplements sit on top of that floor. If the floor is low, no supplement is pulling you up meaningfully.