Can I Take Ashwagandha with Retatrutide?

What Retatrutide Actually Does in the Body

Retatrutide is an investigational once-weekly subcutaneous peptide that activates all three of the GIP, GLP-1, and glucagon receptors simultaneously. That triple agonism distinguishes it from semaglutide (dual GLP-1/GIP) and makes its metabolic footprint broader.

In the Phase 2 dose-escalation trial published in the New England Journal of Medicine (N=338), participants receiving retatrutide 12 mg lost a mean of 17.5% of body weight at 24 weeks and 24.2% at 48 weeks, compared with 2.1% in the placebo group 1. Those are the largest weight-loss figures reported for any injectable agent in a randomized trial at that duration.

GLP-1 and Glucagon Effects on the HPA Axis

The glucagon receptor component is worth attention here. Glucagon activates the hypothalamic-pituitary-adrenal (HPA) axis. Sustained glucagon receptor stimulation can modestly raise cortisol in animal models, though human data from GLP-1/glucagon dual or triple agonists are limited 2. Retatrutide's net cortisol effect in humans has not been reported in primary publications as of mid-2025.

Thyroid C-Cell Signal

GLP-1 receptor agonists activate GLP-1 receptors on thyroid C-cells, raising calcitonin in rodents. The FDA requires all GLP-1 receptor agonists to carry a black-box warning for thyroid C-cell tumor risk, and that warning applies to retatrutide's Investigational New Drug profile as well 3. TSH itself is not directly altered by GLP-1 receptor agonism in most clinical trials, but individual variation exists.

What Ashwagandha Does in the Body

Ashwagandha (Withania somnifera) is a root extract most commonly standardized to 2.5 to 5% withanolides. It is classified as an adaptogen because of its bidirectional effects on stress hormones.

Cortisol Suppression

The most replicated human finding is cortisol reduction. A double-blind RCT (N=64) published in the Indian Journal of Psychological Medicine found that 300 mg twice-daily KSM-66 ashwagandha root extract reduced serum cortisol by 27.9% versus 7.9% in the placebo group over 60 days 4. A separate 8-week crossover trial (N=60) in chronically stressed adults replicated cortisol reductions of 22.2% with 240 mg/day Sensoril ashwagandha 5.

Cortisol suppression at that magnitude can matter during aggressive caloric restriction. Retatrutide drives weight loss partly through glucagon-mediated increases in energy expenditure, and low cortisol states can blunt the counter-regulatory response to hypoglycemia.

Thyroid Hormone Shifts

Ashwagandha has demonstrated thyroid-stimulating activity in two small trials. An 8-week RCT (N=50) in adults with subclinical hypothyroidism found that 600 mg/day of root extract raised T3 by 41.5% and T4 by 19.6% versus minimal changes in placebo 6. That upward shift in thyroid hormones, combined with any background change from retatrutide-class GLP-1 receptor agonism, could push free T4 and T3 outside reference ranges in susceptible patients.

Testosterone and DHEA Effects

A systematic review and meta-analysis of 7 RCTs (total N=245 men) found ashwagandha supplementation raised serum testosterone by a weighted mean of 14.7% compared with placebo 7. A separate trial (N=57) documented a 17% rise in DHEA-S alongside the testosterone increase 8. These anabolic signals interact with body composition in ways that could theoretically complement or complicate retatrutide's muscle-preservation profile.

The Interaction Field: Pharmacokinetic vs. Pharmacodynamic

This is a pharmacodynamic interaction, not a pharmacokinetic one. That distinction matters for how you manage it.

Why Pharmacokinetics Are Likely Not the Problem

Retatrutide is a large peptide (molecular weight approximately 4.6 kDa) that does not pass through cytochrome P450 hepatic metabolism. It is catabolized by peptidases. Ashwagandha withanolides are metabolized primarily through CYP3A4 and CYP2D6 9, but peptide drugs have essentially no CYP3A4 footprint. So dose-separation windows and timing adjustments do not address the actual concern.

Where the Pharmacodynamic Overlap Lives

Three axes converge:

Cortisol. Retatrutide's glucagon component may nudge cortisol upward; ashwagandha reliably drives it downward. Net cortisol could land anywhere depending on dose and individual HPA sensitivity. During rapid weight loss exceeding 1% body weight per week (which retatrutide can produce), adequate cortisol reserve supports metabolic stability.

Thyroid. Ashwagandha raises T3 and T4 in subclinical hypothyroidism. GLP-1 receptor agonists have produced small TSH reductions in some populations. The directional mismatch is not dangerous in isolation, but patients already on levothyroxine who add both agents face compounded variability 10.

Glucose regulation. Retatrutide lowers fasting glucose through GLP-1 and GIP receptor activation. Ashwagandha independently reduces fasting blood glucose in type 2 diabetes (a 12-week RCT, N=67, showed a 12% reduction versus 0.5% placebo) 11. Additive glucose lowering may increase hypoglycemia risk, especially in patients also on sulfonylureas or insulin.

The table below maps the three axes and their clinical significance.

| Axis | Retatrutide Effect | Ashwagandha Effect | Net Concern | |---|---|---|---| | Cortisol | Possible modest rise (glucagon-mediated) | 22 to 28% reduction (replicated) | Unpredictable cortisol reserve during rapid weight loss | | Thyroid (T3/T4) | Minor TSH variability via GLP-1 C-cell signal | T3 +41.5%, T4 +19.6% in subclinical hypothyroidism | Over-range thyroid hormones in susceptible patients | | Fasting glucose | Significant reduction (GIP/GLP-1 agonism) | Modest 12% reduction (additive) | Compounded hypoglycemia risk with concurrent insulin secretagogues | | Testosterone/DHEA | No direct androgenic effect reported | +14.7% testosterone, +17% DHEA-S | Body composition benefits possible, but unclear net anabolic signaling |

Clinical Evidence on GLP-1 Agents and Adrenal Function

No published trial has examined the adrenal axis specifically for retatrutide. Data from the broader GLP-1 class offer the best available proxy. A 2021 meta-analysis of 22 RCTs covering semaglutide, liraglutide, and dulaglutide (total N=14,607) found no significant change in morning cortisol at 26 weeks 12. Glucagon receptor agonism is newer territory: a dedicated glucagon receptor agonist study in healthy volunteers reported transient cortisol elevations of approximately 15% at peak plasma glucagon concentrations 2.

Retatrutide's glucagon component is titrated alongside GLP-1 and GIP. Whether net glucagon-mediated cortisol signaling survives that co-stimulation remains uncharacterized. Until Phase 3 endocrine sub-study data are published, this remains a plausible, not confirmed, concern.

Monitoring Protocol if You Are Already Taking Both

If a patient is currently taking both agents before prescriber review, the priority is assessment, not immediate discontinuation.

Baseline Labs to Order

Providers should obtain the following before continuing the combination:

• TSH and free T4
• Morning cortisol (8 a.m. Draw)
• Fasting plasma glucose and HbA1c
• Total testosterone and DHEA-S (in males or females with androgenic concerns)
• Basic metabolic panel

The Endocrine Society's 2023 obesity pharmacotherapy guidance states that "thyroid function should be assessed at baseline and periodically during treatment with any GLP-1 receptor agonist in patients with pre-existing thyroid disease" 13. Ashwagandha's thyroid-stimulating properties make that recommendation applicable even in patients without known thyroid disease when the supplement is co-administered.

Follow-Up Schedule

A reasonable monitoring cadence for the combination:

• Week 0 (baseline): full panel above
• Week 12: TSH, free T4, morning cortisol, fasting glucose
• Week 24: repeat full panel
• Ongoing: every 12 weeks during active dose escalation of retatrutide, then every 24 weeks at maintenance dose

If TSH falls below 0.5 mIU/L or free T4 rises above the lab reference range, ashwagandha should be paused and thyroid function rechecked in 6 weeks without the supplement.

When to Discontinue Ashwagandha

Hold ashwagandha and consult an endocrinologist if any of the following occur:

• TSH <0.5 mIU/L or free T4 >upper limit of normal on two consecutive draws
• Morning cortisol <5 mcg/dL without other explanation
• Symptomatic hypoglycemia with confirmed glucose <70 mg/dL not explained by concurrent insulin or sulfonylurea

Retatrutide Phase 3 Trials: What to Watch

The TRIUMPH program (Phase 3 trials for retatrutide) is currently recruiting as of mid-2025. TRIUMPH-1 is examining retatrutide in adults with obesity (BMI >30 or >27 with comorbidities) over 72 weeks. TRIUMPH-CVOT examines cardiovascular outcomes. Neither protocol currently includes ashwagandha co-administration as a reported variable 14.

When TRIUMPH data are published, providers should look specifically for thyroid function sub-studies, adrenal axis data, and any supplement co-use analysis in the safety appendices. The Phase 2 data did report that retatrutide produced dose-dependent nausea (up to 56% incidence at 12 mg) and injection site reactions, with no adrenal or thyroid adverse events flagged in the primary safety table 1.

Practical Dose and Timing Considerations

Because this interaction is pharmacodynamic, timing doses apart during the day does not reduce the risk. The overlap in cortisol and thyroid effects is systemic and sustained, not peak-concentration-dependent.

Ashwagandha half-life after oral dosing is approximately 10 hours for the primary withanolide fraction 9. Retatrutide's half-life is approximately 6 days given its weekly subcutaneous dosing schedule. Neither can be "taken at a separate time" to avoid the interaction.

The practical levers are:

• Ashwagandha dose. Cortisol suppression appears dose-dependent. Reducing from 600 mg/day to 300 mg/day may reduce thyroid and cortisol signal while preserving stress-reduction benefits. No titration data exist specifically for combination with retatrutide.
• Ashwagandha formulation. KSM-66 (root-only extract) and Sensoril (root and leaf) have different withanolide profiles. Sensoril at 125 to 250 mg/day produced smaller cortisol changes than KSM-66 at 600 mg/day in head-to-head pharmacokinetic modeling, though no direct trial has compared them 5.
• Patient selection. Patients with pre-existing subclinical hypothyroidism, adrenal insufficiency, or diabetes managed with insulin or sulfonylureas face higher risk and should be counseled more conservatively.

What Patients Ask Their Providers

Patients combining adaptogens with GLP-1 receptor agonists commonly report taking ashwagandha for sleep quality and stress management, two domains that worsen during rapid caloric restriction. The cortisol-lowering and sleep-improving effects of ashwagandha (a 2019 RCT, N=60, found a 72% improvement in Pittsburgh Sleep Quality Index scores versus 29% in placebo) 15 address real symptoms that retatrutide does not treat.

Providers dismissing the supplement outright may reduce adherence to the more clinically significant intervention (retatrutide). A more useful approach: acknowledge the reason the patient is taking ashwagandha, order baseline thyroid and cortisol labs, and set a clear monitoring schedule rather than issuing a blanket prohibition.

A reasonable summary statement for a patient consult note: "Ashwagandha can be continued at or below 300 mg/day while on retatrutide provided TSH, free T4, and morning cortisol are checked at baseline and at 12-week intervals. Discontinue the supplement if thyroid values drift outside reference range or if morning cortisol falls below 5 mcg/dL."