Fish oil vs ashwagandha: what the evidence says about each

No trial has tested fish oil and ashwagandha together — what's known about each comes from separate research, at different doses, in different people. They're also not comparable ingredients: fish oil is a fatty acid supplement, and its largest synthesis of trial data found little or no cardiovascular effect at any studied dose; ashwagandha is an adaptogenic herb with a more consistent trial base specifically for stress and cortisol.

What the evidence doesn't support

It doesn't support a claim that fish oil and ashwagandha work better together than either alone — that comparison has never been run. It doesn't support ranking one "above" the other in general terms, because they're studied for largely different things: fish oil's trial base is concentrated in cardiovascular biomarkers and, at much higher prescription doses, triglycerides; ashwagandha's is concentrated in stress and cortisol. And it doesn't support treating either one as interchangeable with the other based on a shared "wellness supplement" label.

What the trials found

Fish oil's largest body of evidence is cardiovascular. A 2020 Cochrane review pooled 86 randomized controlled trials in 162,796 people, each at least 12 months long, covering long-chain omega-3 doses from 0.5 g/day to more than 5 g/day. It found little or no effect on all-cause mortality or cardiovascular events, and effects did not differ by dose. That's the largest, most consistent synthesis available on fish oil, and its finding is a null one across the entire dose range studied.

Ashwagandha's evidence is different in kind. A 2012 randomized, double-blind, placebo-controlled trial gave 64 adults with a history of chronic stress 600 mg/day of a high-concentration ashwagandha root extract for 60 days; the treatment group had significantly lower stress-scale scores and lower serum cortisol than placebo. A 2024 meta-analysis pooling nine randomized trials in 558 people found ashwagandha outperformed placebo on the Perceived Stress Scale, an anxiety scale, and serum cortisol. Ashwagandha's stress-and-cortisol research is more consistent than fish oil's cardiovascular research, though it comes from a smaller, more recent body of trials.

Neither ingredient's research includes the other, and no study has measured fish oil and ashwagandha given at the same time.

Ingredient	Best evidence	Population	Dose in that evidence
Fish oil	Little or no effect on cardiovascular events or mortality (86 RCTs)	Adults at varying cardiovascular risk	0.5 g/day to 5+ g/day; no dose difference
Ashwagandha	Lower stress-scale scores and cortisol vs placebo (n=64; also a 9-trial, 558-person meta-analysis)	Adults with chronic stress	600 mg/day, 60 days
Both together	No trial exists	—	—

Questions people ask

Should I take fish oil or ashwagandha?

This page doesn't rank the two against each other — they're studied for different things. Fish oil's largest synthesis found little or no cardiovascular benefit at any dose; ashwagandha's trial base is more consistent for stress and cortisol specifically.

Can you take fish oil and ashwagandha together?

There's no trial of the combination, so there's no evidence describing what taking them together adds beyond what each does on its own. Whether it's appropriate for you is a separate safety question, especially with any medications or conditions involved — worth raising with a doctor or pharmacist.

Does fish oil help with stress like ashwagandha does?

Fish oil's research base doesn't include a comparable stress-and-cortisol trial record. Ashwagandha's does. That's a difference in what's been studied, not a statement that fish oil has no effect on stress at all — it simply hasn't been tested for it the way ashwagandha has.

When to talk to a doctor

Chronic stress that affects daily life is worth bringing to a doctor. Neither fish oil nor ashwagandha is a treatment for a stress-related diagnosis, and nothing in the evidence above supports using either, alone or combined, as a substitute for medical evaluation. Ashwagandha in particular should be discussed with a doctor if you're pregnant or nursing, have a thyroid condition, or take other medication.

Related reading: fish oil benefits: what's established and what isn't and fish oil and heart disease: what the research does and doesn't show.