Ashwagandha (Withania somnifera)
One of the most widely used adaptogens — herbs believed to help the body cope with stress. Ashwagandha has a long history in Ayurvedic medicine and is now one of the best-selling supplements globally. The weight-related evidence is specifically about cortisol reduction and stress-driven eating, not direct fat burning. If stress and emotional eating are significant contributors to your weight, the science is more applicable.
Quick read · 3 min
- •Evidence: Weak — limited or inconsistent trial data
- •A randomised controlled trial of 52 adults under chronic stress (600 mg/day KSM-66 ashwagandha, 8 weeks) found a 3.
- •Well tolerated in short-term studies (up to 3 months).
- •Prescription weight loss drugs produce 7–21% weight loss in trials. Most supplements in this category produce less than 2 kg.
Based on clinical trials · No rankings · Every claim linked to source
Last reviewed: March 2026
How it works
Ashwagandha's primary documented effect is reducing cortisol — the body's main stress hormone. Chronically elevated cortisol promotes fat storage (particularly belly fat), increases appetite, drives carbohydrate cravings, and contributes to insulin resistance. By reducing cortisol, ashwagandha may indirectly reduce stress-driven eating, improve sleep quality (which also affects weight), and modestly improve body composition. The withanolides (active compounds) appear to interact with the HPA (hypothalamic-pituitary-adrenal) axis — the body's stress response system.
What the evidence shows
A randomised controlled trial of 52 adults under chronic stress (600 mg/day KSM-66 ashwagandha, 8 weeks) found a 3.0% reduction in body weight and 2.9% reduction in BMI, compared to 1.5% weight reduction and 1.4% BMI reduction with placebo. Serum cortisol significantly decreased; food cravings and emotional eating scores also improved. A broader set of trials confirms the cortisol-lowering and stress-reducing effects (including a 27% reduction in perceived stress in one trial). The weight/body composition effects are modest and most relevant for people who overeat in response to stress. Ashwagandha is not a weight loss drug — it's better understood as a stress-management supplement with a secondary effect on weight in stress-affected individuals.
Safety
Well tolerated in short-term studies (up to 3 months). Most common side effects are mild GI discomfort and drowsiness (which can be beneficial if taken at night). Rare cases of liver injury have been reported — not established as causal but worth noting. Not recommended in pregnancy (may cause uterine contractions). May interact with thyroid medications (ashwagandha can affect thyroid hormone levels), sedatives, and immunosuppressants. People with autoimmune conditions should use with caution as ashwagandha may stimulate the immune system.
Community insights
These are personal experiences shared in public online communities — not medical advice.
“The sleep improvement is often the most noticeable effect — many people report significantly better sleep quality within 1–2 weeks. Better sleep also helps with weight indirectly.”
“Look for KSM-66 or Sensoril — these are the standardised, patented extracts used in the actual clinical trials. Generic 'ashwagandha root powder' may have inconsistent withanolide content.”
“If you're on thyroid medication (levothyroxine etc.), check with your doctor before taking ashwagandha — it can affect thyroid hormone levels.”
Common questions
After reading this page, most people compare this with other supplements, look at prescription options, or check what they can do today without a prescription.