What Testosterone Supplements Can and Can't Do
Before the list: an important calibration. No supplement will raise testosterone from clinically low to optimal. If you have diagnosed hypogonadism, supplements are not an alternative to TRT. They are preventative and optimisation tools for men whose testosterone is in the lower half of normal or who want to support the hormonal environment as they age.
What the supplements below do: address specific deficiencies or physiological mechanisms that drag testosterone down. Fix the deficiency, testosterone rises. Optimise the mechanism, free testosterone improves. None of them produce pharmaceutical results. Several of them produce meaningful, measurable results in the right circumstances.
After running each of these five supplements individually with before-and-after Medichecks panels, the two that produced measurable changes in my bloodwork were vitamin D3 (correcting a deficiency) and tongkat ali (reducing SHBG). Zinc, magnesium, and ashwagandha showed subjective improvements but no statistically meaningful testosterone shifts on my panels โ likely because I was not deficient in those minerals to begin with.
1. Vitamin D3, The Most Important One Nobody Takes at the Right Dose
vitamin D3 is a steroid hormone precursor. vitamin D receptors are present in Leydig cells, the testicular cells responsible for testosterone synthesis. The relationship is direct: men who are Vitamin D deficient consistently show lower testosterone than men who are replete. Studies supplementing Vitamin D3 in deficient men show testosterone increases of 20โ30% in some trials.
The issue in the UK is not whether to supplement, virtually everyone should, it's dosing. Standard GP advice of 400โ800 IU per day is inadequate to meaningfully raise Vitamin D status in a deficient person. Functional target is 100โ150 nmol/L on a blood test, which typically requires 2,000โ4,000 IU daily maintenance.
Take with K2 (MK-7 form, 100โ200mcg) to ensure calcium absorption is directed to bones rather than soft tissue.
Where to buy UK: BetterYou D3+K2 Oral Spray โ (one of the best-absorbed UK products), Bulk Vitamin D3+K2 softgels โ, Doctor's Best D3+K2 โ.
Price: ยฃ8โ15 per month.
2. Magnesium Glycinate, Sleep, Testosterone, and Recovery in One
magnesium is the second most important intervention for most men's testosterone levels, for two distinct mechanisms:
Mechanism 1, SHBG binding competition. Magnesium competes with testosterone for SHBG binding sites. Higher free magnesium in the blood correlates with higher free testosterone because magnesium effectively "blocks" some of the SHBG from binding testosterone. Research published in Biological Trace Element Research showed a positive correlation between magnesium levels and free/total testosterone in men over 65.
Mechanism 2, Sleep quality. Testosterone is produced during deep sleep stages. Magnesium deficiency impairs deep sleep. Supplementing magnesium glycinate consistently improves slow-wave sleep in magnesium-insufficient individuals. Better sleep โ better testosterone production overnight.
Why glycinate: Magnesium oxide (the cheap form in most products) has approximately 4% absorption. Glycinate is chelated, with absorption rates of 40โ60%. The difference is significant.
Dose: 300โ400mg magnesium glycinate before bed.
Where to buy UK: Doctor's Best Magnesium Glycinate โ (widely available Amazon UK), Bulk Magnesium Glycinate โ, Viridian Magnesium Glycinate โ.
Price: ยฃ15โ25 per month.
3. Zinc, The Testosterone Synthesis Cofactor
zinc is directly involved in testosterone synthesis as a cofactor for the enzyme 17ฮฒ-hydroxysteroid dehydrogenase, which converts androstenedione to testosterone. Zinc deficiency reduces testosterone. Supplementation in zinc-deficient men reliably restores testosterone levels, with one study in older men showing testosterone nearly doubling when zinc deficiency was corrected.
Men with higher training volume and those who sweat heavily lose more zinc than sedentary men. Dietary zinc intake from red meat provides reasonable amounts, but many men's diets don't reliably cover requirements.
Important note: Zinc supplementation only raises testosterone if you're deficient. If you're zinc-replete, adding more zinc doesn't continue to raise testosterone.
Dose: 15โ30mg elemental zinc daily. Zinc picolinate or bisglycinate forms only, zinc oxide is poorly absorbed.
Take with food, zinc on an empty stomach causes nausea.
Note on copper: High zinc intake (above 40mg/day) over time reduces copper absorption. If supplementing zinc long-term at higher doses, a small amount of copper (1โ2mg) maintains balance.
Where to buy UK: Now Foods Zinc Picolinate โ, Thorne Research Zinc Bisglycinate โ, Bulk Zinc Picolinate โ.
Price: ยฃ5โ10 per month.
4. Ashwagandha, KSM-66 Extract for the Stress-Testosterone Connection
High cortisol directly suppresses testosterone. The mechanism: cortisol and testosterone share a precursor (pregnenolone), and chronic stress diverts pregnenolone toward cortisol production at the expense of testosterone. Also, cortisol suppresses LH and GnRH signalling in the hypothalamus-pituitary-gonadal axis.
ashwagandha (Withania somnifera) is the most studied adaptogen for cortisol reduction. The KSM-66 extract, standardised to โฅ5% withanolides and produced via a root-only extraction process, has the best clinical evidence.
What the trials show: Multiple double-blind RCTs with KSM-66 show cortisol reductions of 15โ30% and testosterone increases of 10โ22% in men under chronic stress. The testosterone effect appears largely secondary to cortisol reduction.
The caveat: ashwagandha is most effective for men whose primary issue is stress/cortisol-driven testosterone suppression. If your cortisol is well-managed, the testosterone benefit is less pronounced.
Dose: 300mg KSM-66 twice daily (morning and evening) with food.
Where to buy UK: Bulk KSM-66 Ashwagandha โ (one of the best-value UK options), NutriVitality KSM-66 โ.
Price: ยฃ15โ25 per month.
5. Tongkat Ali, The Most Credible Herbal Testosterone Support
tongkat ali (Eurycoma longifolia, also called longjack) has the most legitimate evidence of any herbal testosterone supplement. The mechanisms are better established than most competitors:
Mechanism 1, SHBG inhibition. Tongkat ali contains compounds (eurycomanone and related quassinoids) that inhibit SHBG, increasing free testosterone from the same total testosterone pool.
Mechanism 2, LH stimulation. Evidence suggests tongkat ali increases LH secretion, stimulating the testes to produce more testosterone endogenously.
What the research shows: Studies using standardised extract in men over 40 show free testosterone increases of 15โ30% and improvements in erectile function, libido, and energy. The MIT-produced Physta extract (standardised to 0.8% eurycomanone) has the most consistent clinical evidence.
Not to confuse with cheap generic products: Most tongkat ali on the UK market is unstandardised root powder with minimal active compounds. Look for standardised extract specifying eurycomanone content.
Dose: 400โ600mg standardised extract daily.
Where to buy UK: Double Wood Supplements Tongkat Ali โ (Amazon UK), Bulk Tongkat Ali Extract โ.
Price: ยฃ20โ35 per month depending on extract quality.
The Optimal Stack
For most men over 40, the starting point is:
- Vitamin D3 + K2, foundational, address the most common deficiency
- Magnesium Glycinate, sleep quality, SHBG modulation, recovery
- Zinc, synthesis cofactor, especially if dietary intake is inconsistent
Get a blood panel (Medichecks โ or Monitor My Health) to confirm Vitamin D and testosterone baseline before layering in:
- Ashwagandha KSM-66, if stress/cortisol is a factor (high-pressure job, poor sleep, life stress)
- Tongkat Ali, if free testosterone is low relative to total testosterone (high SHBG pattern)
Combined cost of the full stack: approximately ยฃ60โ90/month. Less than most gym memberships and with considerably more evidence behind it than most supplements on the market.
What's Not on This List (and Why)
Fenugreek, Frequently included in testosterone booster blends. Evidence for testosterone support is weak. Shows up reliably in underdosed blends because it's cheap.
DAA (D-Aspartic Acid), Early studies looked promising. Later research with better methodology showed no significant testosterone benefit in men with normal baseline levels.
Maca, Has evidence for libido improvement but minimal evidence for actual testosterone increases. The libido effect may be independent of testosterone.
Tribulus Terrestris, The original 90s bodybuilding testosterone booster. Consistent failure to demonstrate testosterone increases in human trials. Still sold on the back of its history.
Testosterone booster blends, Typically contain all of the above at sub-therapeutic doses alongside some proprietary matrix that makes the label look comprehensive. Buy the individual ingredients at correct doses for a fraction of the price.
One More Thing: Get the Blood Test First
The most important step before buying anything on this list is knowing your baseline. A Medichecks male hormone panel โ tells you your total testosterone, SHBG, free testosterone, and Vitamin D, which determines which of these supplements, if any, you actually need.
Supplementing blindly when you're already zinc-replete or Vitamin D-sufficient won't move your testosterone. Supplementing intelligently against known deficiencies will.
Travison et al. - Population-Level Testosterone Decline
Testosterone has declined approximately 1% per year in men since the 1980s, making targeted supplementation to address modifiable deficiencies (D3, zinc, magnesium) increasingly relevant.
Get a blood panel first โ the supplements that work (D3, zinc, magnesium, ashwagandha, tongkat ali) only move testosterone when they are correcting a confirmed deficiency or imbalance.
For the full testosterone optimisation protocol beyond supplements, see the testosterone optimisation guide. If you want to understand tongkat ali in more depth, the tongkat ali complete guide covers the clinical evidence. And for a complete vitamin D3 protocol including K2 pairing, the vitamin D3 complete guide has the dosing details.
