Ashwagandha (Withania somnifera)

Why cortisol matters for testosterone

Cortisol and testosterone are functionally antagonistic. Sustained glucocorticoid elevation suppresses gonadal steroidogenesis at several points along the hypothalamic-pituitary-gonadal axis. Any intervention that reliably lowers chronic cortisol therefore has a plausible indirect route to supporting testosterone.

This is an indirect mechanism and worth labelling as such. Ashwagandha is not a testosterone precursor. It removes a brake rather than pressing an accelerator.

The trial evidence

The most cited study is a randomized, double-blind, placebo-controlled trial in 64 adults with a history of chronic stress. Participants receiving 300mg of a standardized root extract twice daily for 60 days showed a reduction in serum cortisol of approximately 28% relative to baseline, alongside significant improvements in perceived stress scores.¹

This is not isolated. A 2019 crossover trial in overweight men aged 40 to 70 reported improvements in DHEA-S and testosterone alongside reduced fatigue.² A separate 2019 study found dose-dependent cortisol reductions at both 250mg and 600mg daily.³ A 2022 systematic review and meta-analysis pooling the available randomized trials concluded that supplementation significantly reduced both cortisol and anxiety measures.⁴

By the standards of this category, where most ingredients rest on a single small study or on animal data, that is an unusually consistent picture.

The caveats

• Trial size. Most enrol between 50 and 130 participants over 8 to 12 weeks. Consistent, but not large-scale evidence.
• Funding. Several of the key trials were funded by extract manufacturers. This does not invalidate them, and industry funding is the norm in nutritional research, but independent replication would strengthen the case considerably.
• Baseline dependence. Effects are clearest in participants with elevated baseline cortisol. In men with normal cortisol, expect less.
• Extract type. Trials used root extracts standardized to withanolide content. Leaf material and unstandardized powder are different products.

Dosing

The effective range across trials is 240 to 600mg per day of root extract standardized to withanolides, typically 5%, taken for a minimum of eight weeks. Most protocols split the dose between morning and evening.

Two label patterns should prompt scepticism. The first is a proprietary "calm" or "stress" blend with no individual ashwagandha figure, which makes verification impossible. The second is a token 50mg inclusion in a product whose front label emphasises stress support, an order of magnitude below anything studied.

Safety

Generally well tolerated in trials at these doses. Gastrointestinal upset and drowsiness are the most commonly reported effects. Ashwagandha can influence thyroid hormone levels, so anyone with thyroid disease or on thyroid medication should consult a clinician first. It is not appropriate during pregnancy. Isolated cases of liver injury have been reported in the literature, which is an argument for third-party tested material from a reputable manufacturer rather than a reason to avoid it.

Bottom line

Standardized ashwagandha root extract, at 240 to 600mg daily for at least eight weeks, reliably lowers cortisol in stressed adults. The gap between that finding and most products on the shelf is dose and standardization. Which commercial formulas actually meet the studied dose is covered in our comparative review.