Affiliate links: as an Amazon Associate and through other programs, we earn from qualifying purchases, at no extra cost to you. Learn more.
In This Article
Supplements That Lower Cortisol: The Short Answer
OUR TOP CORTISOL-SUPPORT PICKS · affiliate links, we may earn a commission
1. Ashwagandha (KSM-66 or Sensoril extract): in a 2025 review of 7 trials it lowered blood cortisol, although perceived stress did not change significantly (Albalawi, 2025). Trials used 300-600 mg a day. See it on Amazon →
2. Magnesium Glycinate: no good trial shows that it lowers cortisol. It only makes sense if your diet is low in magnesium, and supplements should stay at or below 350 mg a day. See it on Amazon →
3. L-Theanine: in a 4-week trial, 200 mg a day improved stress-related symptom scores and sleep quality (Hidese et al., 2019). See it on Amazon →
Deep dives: our full ashwagandha guide and the 2026 sleep stack (one night of short sleep raised evening cortisol in a lab study: Leproult et al., 1997).
Ashwagandha has the most evidence for lowering cortisol, and even there the effect is modest. A 2025 review of 7 trials found that blood cortisol fell by 1.16 µg/dL on average, while perceived stress did not change significantly (Albalawi, 2025). Phosphatidylserine blunted the rise in cortisol after exercise in two very small studies, and the evidence for magnesium and vitamin C is thin. Sleep comes first.
- Ashwagandha root extract: 300-600 mg a day in trials; a modest drop in cortisol in a 2025 review of 7 trials
- Phosphatidylserine: 600-800 mg a day for 10 days lowered the cortisol rise after exercise in two very small studies
- L-theanine: 200 mg a day; small trials on self-rated stress
- Magnesium and vitamin C: weak or indirect evidence for cortisol
What the research shows for each option
Ashwagandha root extract
- Dose in trials: 300 mg twice a day (600 mg a day) of a standardized root extract
- What the research found: in 64 adults with chronic stress, 60 days of a root extract lowered serum cortisol and stress scores more than placebo (Chandrasekhar et al., 2012). A 2025 review of 7 trials found an average drop of 1.16 µg/dL in cortisol, with no significant change in perceived stress (Albalawi, 2025).
- Watch out for: the NIH says it appears safe for up to about 3 months; rare cases of liver injury have been reported (Björnsson et al., 2020). Avoid it in pregnancy, and ask your doctor first if you have a thyroid condition or take sedatives or thyroid, blood pressure, diabetes or immune-suppressing medicines (NIH ODS).
Phosphatidylserine
- Dose in studies: 600-800 mg a day for 10 days, in small exercise studies
- What the research found: in 10 healthy men, 600 mg a day for 10 days lowered peak cortisol after cycling by about 39% compared with placebo (Starks et al., 2008). An older study in 9 men used 800 mg a day of phosphatidylserine made from cow brain and also blunted the cortisol response to exercise (Monteleone et al., 1992). These are tiny studies of exercise stress, not everyday stress.
- Watch out for: long-term safety data are limited, so ask your doctor first if you take any medication.
Magnesium
- Dose: no more than 350 mg a day from supplements (the NIH upper limit); magnesium from food does not count toward it
- What the research found: a systematic review of 18 studies found hints that magnesium may help self-rated anxiety in people prone to it, but the evidence was poor and no study used a validated stress measure (Boyle et al., 2017). We found no good trial showing that it lowers cortisol.
- Watch out for: diarrhea at higher doses. If you have kidney disease, ask your doctor first, because healthy kidneys are what clear the extra magnesium (NIH ODS).
Vitamin C
- Dose in studies: 1,500-3,000 mg a day in short trials; the adult upper limit is 2,000 mg a day
- What the research found: runners taking 1,500 mg a day had lower cortisol right after a 90 km race than runners on placebo or 500 mg (Peters et al., 2001). In 120 young adults, 3,000 mg a day for 14 days lowered blood pressure and self-rated stress during a public speaking test and sped up cortisol recovery, but did not reduce the overall cortisol response (Brody et al., 2002). “Adrenal support” is a marketing term, not a proven effect.
- Watch out for: above 1 g a day, less than half is absorbed, and high doses can cause diarrhea and stomach cramps (NIH ODS).
Also worth knowing: rhodiola and L-theanine
Rhodiola (SHR-5 extract). In a 4-week placebo-controlled trial in people with stress-related fatigue, the SHR-5 extract improved burnout scores and attention and lowered the cortisol response to waking compared with placebo (Olsson et al., 2009). The evidence comes from small trials, so treat it as an option for demanding periods rather than a daily staple. Search Amazon for standardized rhodiola extracts (the exact SHR-5 extract from that trial was not sold on Amazon US when we checked on October 15, 2026; standardized extracts list rosavins and salidroside on the label)
L-theanine. In a crossover trial of 34 healthy adults, an L-theanine-based drink lowered self-rated stress one hour after dosing and the salivary cortisol response to a stressor three hours after dosing (White et al., 2016). In a 4-week randomized trial in healthy adults, daily L-theanine improved stress-related symptom scores and sleep quality compared with placebo (Hidese et al., 2019). See L-theanine on Amazon
Get our free supplement cheat sheet.
One page: typical doses, timing and upper limits for ten well-studied supplements. No upsell.
🔒 No spam. Unsubscribe anytime. We send 1-2 emails/month max.
Lifestyle Comes First
No supplement makes up for short sleep. In a laboratory study of young men, one night of partial or total sleep loss raised cortisol the following evening by 37% and 45% (Leproult et al., 1997). Regular sleep, daily movement, morning daylight and keeping caffeine to the morning are the base; supplements are a small extra on top.
If you suspect a cortisol disorder, see a doctor: it is diagnosed with medical tests, not with symptom checklists.
How the options compare
Doses are the ones used in the studies above. None of these supplements is a treatment for a medical cortisol disorder.
| Supplement | Dose used in studies | Evidence on cortisol |
|---|---|---|
| Ashwagandha root extract | 300-600 mg a day | Modest drop in a review of 7 small trials |
| Phosphatidylserine | 600-800 mg a day | Lower cortisol after exercise in two very small studies |
| L-theanine | 200 mg a day | Lower cortisol response to a lab stressor in one small trial of a theanine drink |
| Magnesium | Up to 350 mg a day | No good trials |
| Vitamin C | Up to 2,000 mg a day | Mixed results in small, high-dose studies |
Should you combine them
No trial has tested these supplements together, so a “stack” is guesswork. If you want to try one, start with a single product for the length of time used in the trials (4 to 8 weeks for ashwagandha and L-theanine), and note how you sleep and feel before adding anything else.
Do not combine ashwagandha with sleeping pills or other sedatives without asking your doctor, and count every product that contains magnesium toward the 350 mg daily limit for supplements.
How to choose a product
- Ashwagandha: pick a root extract that names the extract and its withanolide content on the label. The 2012 trial above used a full-spectrum root extract at 300 mg twice a day.
- Phosphatidylserine: check the source on the label (often soy or sunflower). The 1992 study used phosphatidylserine made from cow brain, so its results may not apply to plant-based products.
- Doses: check the amount per serving and avoid proprietary blends that hide how much of each herb you get.
- Quality seals: a USP Verified or NSF mark means an independent lab checked that the label matches the contents. It does not show that the product works.
- Skip “adrenal fatigue” products: a systematic review of 58 studies found no evidence that adrenal fatigue is a real medical condition (Cadegiani and Kater, 2016).
Side effects, interactions and safety
Ashwagandha
In trials, side effects were usually mild: stomach upset, loose stools, nausea and drowsiness. The NIH says it appears safe for up to about 3 months, but long-term safety is unknown. It also notes rare liver problems, possible effects on thyroid function, and possible interactions with thyroid, diabetes, blood pressure, immune-suppressing and sedative medicines. Some experts advise against it in pregnancy and for men with hormone-sensitive prostate cancer (NIH ODS).
Magnesium and vitamin C
High doses of either can cause diarrhea. Take tetracycline or quinolone antibiotics at least 2 hours before, or 4 to 6 hours after, a magnesium supplement, and keep magnesium at least 2 hours apart from bisphosphonates such as alendronate (NIH ODS). Vitamin C supplements may interact with some chemotherapy drugs and with statins (NIH ODS).
Rhodiola
The NIH considers it possibly safe for up to 12 weeks. Reported side effects include dizziness, headache and insomnia, and an interaction with the blood pressure drug losartan has been reported (NCCIH).
Frequently Asked Questions
Which supplement lowers cortisol the most?
Ashwagandha root extract has the most trials, and its effect is modest: cortisol fell, but how stressed people felt did not change significantly (Albalawi, 2025). The other options have smaller or weaker studies.
How long does ashwagandha take to work?
The trial above measured cortisol after 60 days (Chandrasekhar et al., 2012). Give it about 8 weeks before judging it, and do not go past about 3 months without your doctor, because long-term safety is unknown.
Is adrenal fatigue real?
No. A systematic review found no evidence that “adrenal fatigue” is a real medical condition (Cadegiani and Kater, 2016). Ongoing tiredness has many possible causes, and a doctor can check for them.
Should I test my cortisol at home first?
Usually not. Cortisol changes across the day, so a single reading tells you little. If your doctor suspects an adrenal or pituitary problem, they will order the right tests.
Bottom Line
Sleep matters more than any capsule: one night of short sleep raised evening cortisol by 37 to 45% in a lab study (Leproult et al., 1997). If you still want a supplement, ashwagandha root extract has the most evidence, but its effect on cortisol is modest and it is not for everyone. Phosphatidylserine and L-theanine have only small studies, and magnesium and vitamin C have little direct evidence for cortisol.
