Several supplements have meaningful evidence behind them for lowering cortisol, with ashwagandha, phosphatidylserine, and omega-3 fatty acids showing the strongest results in clinical trials. The reductions aren’t subtle: ashwagandha has been shown to cut morning cortisol by 23%, and high-dose omega-3s can lower overall cortisol by 19%. But the effective doses, timelines, and caveats matter, so here’s what the research actually supports.
Ashwagandha
Ashwagandha is the most studied supplement for cortisol reduction, and it delivers the most consistent results. A randomized controlled trial published in the journal Medicine found that participants taking ashwagandha root extract experienced a 23% reduction in fasting morning cortisol over the study period, while the placebo group saw a slight (0.5%) increase. Most trials use standardized extracts like KSM-66 or Shenoden at doses between 300 and 600 mg per day.
The mechanism involves your body’s central stress response system. Ashwagandha appears to calm the chain reaction that starts in the brain when you perceive stress, reducing the release of the initial signaling hormone that ultimately tells your adrenal glands to pump out cortisol. This makes it what researchers call an “adaptogen,” meaning it helps your body regulate its stress response rather than simply suppressing a single hormone.
There are real contraindications to be aware of. The National Center for Complementary and Integrative Health advises against ashwagandha if you have a thyroid disorder, an autoimmune condition, or hormone-sensitive prostate cancer. It can interact with medications for diabetes, high blood pressure, seizures, and thyroid conditions, as well as sedatives and immunosuppressants. It should be avoided during pregnancy and breastfeeding.
Phosphatidylserine
Phosphatidylserine (PS) is a fat-based compound found naturally in cell membranes, and it has a specific talent for blunting cortisol spikes triggered by physical and mental stress. The effective dose matters a lot here. In one study, 800 mg per day of bovine-derived PS reduced the cortisol response to cycling exercise by 30%, while 400 mg had no significant effect. Soy-derived PS at 800 mg lowered the cortisol response to intense resistance training by about 20%.
A study testing 600 mg per day of soy-derived PS for 10 days found it blunted cortisol levels both before and during exercise. Interestingly, a separate trial using a soy lecithin complex found that 400 mg per day produced a pronounced reduction in both cortisol and its upstream signaling hormone, while higher doses of 600 and 800 mg did not replicate that effect. This inconsistency across formulations means the type of PS product you choose likely influences results. For most people, 600 mg per day for at least 10 days is a reasonable starting point based on the weight of the evidence.
Omega-3 Fatty Acids
High-dose fish oil can lower your overall cortisol output, but only at doses most people aren’t taking. A randomized controlled trial in midlife adults found that 2.5 grams per day of omega-3s produced 19% lower total cortisol levels during a stress test compared to placebo, in a clear dose-response pattern. The lower dose of 1.25 grams per day had no significant effect on cortisol at all.
One nuance: the omega-3 group didn’t show a smaller cortisol spike in response to stress. Their overall cortisol levels were simply lower throughout the entire testing period. This suggests omega-3s may help keep baseline cortisol in check rather than blocking the acute stress response. Most standard fish oil capsules contain about 300 mg of combined omega-3s, so reaching 2.5 grams per day typically requires a concentrated formula or multiple capsules.
Rhodiola Rosea
Rhodiola rosea works through its active compound salidroside, which reduces activity in the part of the hypothalamus responsible for kicking off the stress hormone cascade. Specifically, it dials down the expression of the signaling hormone (CRH) that starts the whole chain, limiting adrenal activation before it ramps up. Animal studies consistently show that rhodiola extract can calm an overactive stress response system and reduce circulating stress hormones.
The human evidence for rhodiola is less precise than for ashwagandha or PS. Most trials report improvements in perceived stress, fatigue, and mood rather than measuring cortisol directly. Typical study doses range from 200 to 600 mg per day of standardized extract. It’s generally well tolerated, though it can have mild stimulating effects, so morning dosing makes the most sense.
Magnesium
Magnesium doesn’t lower cortisol the way ashwagandha does, but being deficient in it can raise cortisol on its own. Animal research shows that a magnesium-deficient diet increases the production of the brain’s initial stress signaling hormone and elevates circulating stress hormones. A human intervention trial using 350 mg of magnesium citrate daily found improvements in the body’s processing and metabolism of cortisol-type hormones over time.
Roughly half of adults in the U.S. don’t meet the recommended daily intake for magnesium, which makes this one of the more practical interventions on the list. If your diet is low in leafy greens, nuts, seeds, and whole grains, correcting a magnesium shortfall may help normalize your cortisol regulation without needing a more targeted supplement. Magnesium glycinate and magnesium citrate are the most commonly used forms in research.
Vitamin C
High-dose vitamin C won’t prevent a cortisol spike when you’re stressed, but it helps your body recover from one faster. In a trial of 120 healthy adults, those taking 3,000 mg per day of sustained-release vitamin C for two weeks showed faster cortisol recovery after a standardized stress test involving public speaking and mental arithmetic. Their blood pressure and subjective stress responses were also lower than the placebo group.
This makes vitamin C more of a recovery aid than a cortisol blocker. If your cortisol tends to stay elevated long after the stressful event is over, rather than returning to baseline quickly, vitamin C may help with that specific pattern.
How Long Before You See Results
Most cortisol-lowering supplements need at least two to four weeks of consistent daily use before producing measurable changes. Phosphatidylserine works on the faster end, with cortisol blunting observed after just 10 days in some trials. Ashwagandha studies typically run 8 to 12 weeks, with cortisol reductions appearing within the first month. Omega-3 trials showing cortisol effects lasted four months, though changes may begin earlier.
The supplements that act on baseline cortisol levels (ashwagandha, omega-3s, magnesium) generally take longer to show effects than those that blunt acute cortisol spikes (phosphatidylserine). If you’re dealing with chronically elevated cortisol from ongoing life stress, plan on at least a month of consistent use before evaluating whether something is working for you.
Timing and Practical Considerations
Cortisol follows a natural daily rhythm, peaking within 30 to 60 minutes of waking and dropping to its lowest point around midnight. No strong evidence points to a specific time of day being universally better for taking cortisol-lowering supplements, with the exception of melatonin (0.5 to 5 mg at bedtime), which can modulate overnight cortisol production by acting directly on receptors in the adrenal glands.
For the supplements listed above, consistency matters more than timing. That said, rhodiola is mildly stimulating and is best taken in the morning. Ashwagandha can be taken morning or evening. Phosphatidylserine is often taken with meals due to its fat-soluble nature, and some people prefer it before exercise if that’s when their cortisol spikes are most problematic. Magnesium glycinate taken in the evening can support sleep quality, which itself is one of the most powerful regulators of healthy cortisol patterns.