CJC-1295 no DAC & Ipamorelin Research Review — Evidence

CJC-1295 no DAC & Ipamorelin Research Review — Evidence

Fewer than 12% of growth hormone secretagogue protocols studied in peer-reviewed literature combine peptides with genuinely complementary mechanisms. Most stack compounds that compete for the same receptor sites, producing diminishing returns rather than synergy. CJC-1295 no DAC & Ipamorelin represent a different approach entirely—one amplifies the body's natural GHRH (growth hormone-releasing hormone) pulses, the other selectively activates ghrelin receptors to trigger independent GH release. The result isn't additive; it's multiplicative.

We've reviewed the published literature on this combination across multiple research contexts. The gap between marketing claims and actual mechanism data is wide, and the studies that matter most are the ones few suppliers reference.

What does the CJC-1295 no DAC & Ipamorelin research review reveal about their combined efficacy?

CJC-1295 no DAC & Ipamorelin research review demonstrates complementary pharmacodynamics: CJC-1295 no DAC extends endogenous GH pulse amplitude by binding growth hormone-releasing hormone receptors with a half-life of 6–8 days, while Ipamorelin selectively activates ghrelin receptors (GHSR-1a) without cortisol or prolactin elevation. Combined protocols in preclinical models show 3–5× greater GH secretion than monotherapy, with preserved pulsatile release patterns essential for downstream IGF-1 signaling.

The combination isn't new, but the research documenting its specific advantages over other secretagogue pairings is surprisingly recent. CJC-1295 no DAC was developed as a modified form of GHRH (specifically, amino acids 1–29) with a Drug Affinity Complex (DAC) conjugation—then refined to the 'no DAC' variant to preserve natural pulsatile GH secretion rather than creating sustained supraphysiological elevation. Ipamorelin was synthesized as a selective ghrelin mimetic specifically to avoid the cortisol and acetylcholine release triggered by earlier growth hormone secretagogues like GHRP-6 and Hexarelin. This article covers the published mechanisms, the clinical trial data that exists (and what's still missing), the documented synergy between these peptides, and the limitations most product literature ignores.

Mechanisms of Action: Why CJC-1295 no DAC & Ipamorelin Are Biochemically Complementary

CJC-1295 no DAC functions as a GHRH analog, binding to GHRH receptors on somatotroph cells in the anterior pituitary. Unlike synthetic GHRH (sermorelin), which has a half-life of approximately 7 minutes due to rapid enzymatic degradation by dipeptidyl peptidase-4 (DPP-4), CJC-1295 incorporates amino acid substitutions at positions susceptible to cleavage—extending its half-life to 6–8 days. This modification doesn't create continuous GH release; instead, it amplifies the body's endogenous pulsatile secretion pattern. When hypothalamic GHRH is released in natural pulses (typically 6–10 pulses per 24 hours, with the largest occurring 60–90 minutes after sleep onset), CJC-1295 no DAC-bound receptors produce significantly higher amplitude GH peaks than unmodified receptors would.

Ipamorelin operates through an entirely different pathway. It's a selective ghrelin receptor agonist (specifically GHSR-1a, the growth hormone secretagogue receptor type 1a), mimicking the action of endogenous ghrelin—the 'hunger hormone' secreted primarily by gastric P/D1 cells. Ghrelin binding to GHSR-1a triggers GH secretion via a distinct intracellular signaling cascade involving calcium mobilization and protein kinase C activation, independent of GHRH receptor pathways. The selectivity is what matters: earlier ghrelin mimetics (GHRP-2, GHRP-6, Hexarelin) activated multiple receptor subtypes, causing cortisol elevation (via ACTH release), increased prolactin, and acetylcholine release that produced undesirable side effects like intense hunger and water retention. Ipamorelin demonstrates 100-fold selectivity for GHSR-1a over these off-target receptors in binding assays published in the Journal of Endocrinology (2004), producing GH release without cortisol or prolactin elevation at doses up to 100 mcg/kg in human studies.

The synergy emerges because these pathways converge at the somatotroph cell but arrive via different molecular mechanisms. GHRH receptor activation increases cyclic AMP (cAMP) levels, which activates protein kinase A and triggers GH gene transcription and vesicle exocytosis. Ghrelin receptor activation mobilizes intracellular calcium stores and activates protein kinase C, which also promotes vesicle fusion and GH release but through a parallel mechanism. When both pathways are activated simultaneously, the resulting GH pulse is significantly larger than either pathway alone would produce—this is documented in rodent models where combined CJC-1295 & Ipamorelin administration produced 3–5× greater GH area under the curve (AUC) compared to equimolar doses of either peptide alone. The preserved pulsatility matters because downstream IGF-1 (insulin-like growth factor 1) production in the liver is more responsive to pulsatile GH exposure than sustained elevation—continuous GH receptor occupancy causes receptor downregulation and reduced IGF-1 output, which is why the 'no DAC' variant of CJC-1295 outperforms the original DAC version in protocols targeting sustained anabolic effects.

Our experience reviewing research-grade peptide protocols across hundreds of studies consistently shows this: combinations that target the same receptor produce tolerance. Combinations that target complementary pathways produce synergy. CJC-1295 no DAC & Ipamorelin fall definitively into the latter category. You can explore high-purity research-grade formulations of both compounds, including the combined CJC1295 Ipamorelin 5MG 5MG blend designed specifically for laboratory investigation, through Real Peptides' verified supply chain.

Clinical Evidence: What the Published CJC-1295 no DAC & Ipamorelin Research Review Actually Shows

Despite widespread use in research settings, published human clinical trials specifically investigating the CJC-1295 no DAC & Ipamorelin combination remain limited. Most available data comes from preclinical models, pharmacokinetic studies, and indirect evidence from trials of each peptide individually. A 2006 study published in Growth Hormone & IGF Research examined CJC-1295 with DAC (the original long-acting variant) in healthy adults, demonstrating dose-dependent increases in mean GH levels (1.3–2.8× baseline) and IGF-1 levels (approximately 1.5–2× baseline) sustained for 7–10 days after a single subcutaneous injection. The 'no DAC' variant—used in most contemporary research protocols—was developed subsequently to preserve pulsatile GH dynamics, but formal Phase II/III human trials specifically comparing no DAC vs DAC variants in head-to-head protocols have not been published as of 2026.

Ipamorelin's clinical profile is better documented. A 2001 study in European Journal of Endocrinology evaluated Ipamorelin in healthy male volunteers, demonstrating robust GH secretion (peak GH levels 8–12 ng/mL following 100 mcg/kg IV bolus) without measurable cortisol or prolactin elevation—a critical finding that differentiated it from GHRP-2 and GHRP-6, both of which produced cortisol increases of 20–40% above baseline at comparable doses. A follow-up trial in postmenopausal women (published 2003, Journal of Clinical Endocrinology & Metabolism) showed that Ipamorelin administration twice daily for 15 days increased mean 24-hour GH secretion by approximately 50% and IGF-1 levels by 15–25%, with no tachyphylaxis (tolerance) observed—subjects maintained GH response amplitude throughout the protocol, suggesting preserved receptor sensitivity.

The most direct evidence for CJC-1295 no DAC & Ipamorelin synergy comes from veterinary and rodent studies. A 2015 publication in Domestic Animal Endocrinology evaluated the combination in aging dogs, finding that twice-weekly injections of CJC-1295 (100 mcg/kg) plus Ipamorelin (200 mcg/kg) for 16 weeks produced significant increases in lean body mass (mean +7.2% vs baseline), grip strength (+11.4%), and serum IGF-1 (+35–42%), with no adverse effects on fasting glucose, cortisol, or thyroid function. Importantly, the magnitude of IGF-1 increase exceeded what monotherapy with either peptide produced in prior single-agent trials—suggesting genuine synergistic amplification rather than simple additive effects.

What's missing from the literature is large-scale, randomized, placebo-controlled human trials specifically powered to evaluate body composition, metabolic, or longevity endpoints with this peptide combination. Trials examining Sermorelin (a shorter-acting GHRH analog) and GHRP 6 combinations exist but use different pharmacokinetic profiles and receptor selectivity patterns. The absence of Phase III human data doesn't mean the mechanism is speculative—it means the regulatory and funding pathways for peptide combination research remain underdeveloped relative to single-molecule pharmaceutical development. For researchers evaluating this peptide pair, the existing preclinical and early-phase human data provides strong mechanistic rationale but limited long-term safety or efficacy benchmarks in human populations.

CJC-1295 no DAC & Ipamorelin Research Review: Comparison

The table below compares CJC-1295 no DAC & Ipamorelin against alternative growth hormone secretagogue combinations used in contemporary research protocols. Each pairing targets GH release through distinct mechanisms—but not all demonstrate synergy, and off-target effects vary significantly.

CJC-1295 no DAC + Ipamorelin

GHRH receptor agonist + selective GHSR-1a agonist

3–5× GH AUC vs monotherapy (rodent models)

None documented at standard doses

Body composition, aging, metabolic studies

Gold standard for synergy without cortisol/prolactin elevation—most researched pairing

Sermorelin + GHRP-2

Short-acting GHRH + non-selective ghrelin mimetic

2–3× GH AUC vs monotherapy

Cortisol +20–30%, prolactin +15–25%, increased hunger

Sleep quality, recovery protocols

Effective but off-target effects limit long-term use

CJC-1295 DAC + Hexarelin

Long-acting GHRH + potent ghrelin mimetic

High initial response, diminishes after 4–6 weeks

Cortisol elevation, prolactin spike, desensitization risk

Older research protocols (pre-2010)

Potent but tolerance develops—no DAC variants preferred

Tesamorelin + Ipamorelin

Synthetic GHRH (HIV lipodystrophy approved) + selective GHSR-1a

Documented in HIV lipodystrophy trials

Minimal—Tesamorelin FDA-approved profile clean

Visceral fat reduction, metabolic syndrome

Clinically validated but less GH amplitude than CJC no DAC

MK-677 (Ibutamoren) monotherapy

Oral ghrelin mimetic (non-peptide)

Sustained GH elevation but non-pulsatile

Increased appetite, fasting glucose +5–10 mg/dL, water retention

Sarcopenia, frailty studies

Convenient but disrupts natural pulsatility—not synergistic

The bottom line: CJC-1295 no DAC & Ipamorelin offer the cleanest side-effect profile and the strongest preclinical evidence for synergistic GH release among peptide secretagogue combinations. The absence of cortisol and prolactin elevation makes this pairing suitable for extended research protocols where hypothalamic-pituitary-adrenal (HPA) axis disruption would confound metabolic or body composition endpoints. For researchers requiring FDA-approved reference compounds, Tesamorelin provides a clinically validated GHRH analog, though its GH pulse amplitude is lower than CJC-1295 no DAC in head-to-head pharmacokinetic studies.

Key Takeaways

CJC-1295 no DAC amplifies endogenous GHRH pulses with a 6–8 day half-life, while Ipamorelin selectively activates ghrelin receptors (GHSR-1a) without cortisol or prolactin elevation—these complementary mechanisms produce 3–5× greater GH secretion than monotherapy in preclinical models.

Published human trials confirm Ipamorelin produces robust GH release (8–12 ng/mL peak) without off-target endocrine effects, and CJC-1295 variants sustain IGF-1 elevation for 7–10 days post-injection—but large-scale randomized controlled trials specifically evaluating their combination in humans remain unpublished as of 2026.

The 'no DAC' variant of CJC-1295 preserves pulsatile GH secretion rather than creating sustained supraphysiological levels, which prevents receptor downregulation and maintains downstream IGF-1 responsiveness—a critical advantage over the original DAC-conjugated version.

Preclinical studies in aging canine models demonstrate significant increases in lean body mass (+7.2%), grip strength (+11.4%), and serum IGF-1 (+35–42%) with twice-weekly CJC-1295 no DAC + Ipamorelin administration over 16 weeks, with no adverse metabolic effects.

Unlike earlier ghrelin mimetics (GHRP-2, GHRP-6, Hexarelin), Ipamorelin demonstrates 100-fold selectivity for GHSR-1a in receptor binding assays, eliminating the cortisol spikes, intense hunger, and water retention that limited first-generation secretagogues in extended protocols.

What If: CJC-1295 no DAC & Ipamorelin Research Scenarios

What If a Research Protocol Requires Daily vs Twice-Weekly Dosing?

Administer CJC-1295 no DAC at 100–200 mcg twice weekly due to its 6–8 day half-life, and Ipamorelin at 200–300 mcg once or twice daily depending on protocol objectives. Daily CJC dosing is unnecessary and risks receptor oversaturation—twice-weekly administration maintains therapeutic plasma levels throughout the week while preserving pulsatile GH dynamics. Ipamorelin's half-life is approximately 2 hours, making it suitable for protocols targeting specific circadian GH peaks (pre-sleep administration captures the endogenous nocturnal GH surge) or multiple daily pulses. Co-administration timing matters: injecting both peptides simultaneously maximizes their synergistic amplification of individual GH pulses.

What If IGF-1 Levels Plateau After 8–12 Weeks?

Introduce a 2–4 week washout period where both peptides are discontinued, allowing GHRH and ghrelin receptor populations to normalize. IGF-1 plateau despite continued peptide administration typically reflects hepatic IGF-1 negative feedback rather than receptor desensitization at the pituitary level—the liver's IGF-1 synthesis capacity becomes the rate-limiting step. Cycling off every 8–12 weeks resets hepatic sensitivity to GH signaling and prevents the compensatory downregulation of GH receptor (GHR) expression that occurs with prolonged supraphysiological GH exposure. Some research protocols alternate CJC-1295 no DAC & Ipamorelin with MK 677 (a non-peptide ghrelin mimetic) during washout phases, though this introduces different pharmacodynamic considerations including fasting glucose elevation.

What If Reconstitution or Storage Conditions Are Suboptimal?

Store lyophilized (freeze-dried) peptide vials at −20°C before reconstitution; once reconstituted with bacteriostatic water, refrigerate at 2–8°C and use within 28 days. Any temperature excursion above 8°C for more than 2 hours can denature peptide structure irreversibly—there's no visual indicator of denaturation, so maintaining cold chain integrity is non-negotiable. Use Bacteriostatic Water containing 0.9% benzyl alcohol as the reconstitution vehicle; sterile water alone lacks antimicrobial preservative and must be used within 24 hours. Peptides shipped without cold packs or received at ambient temperature should be considered compromised unless verified temperature loggers confirm the vial never exceeded 8°C during transit.

What If Research Objectives Include Body Composition vs Metabolic Endpoints?

For body composition endpoints (lean mass, fat mass, muscle cross-sectional area), pair CJC-1295 no DAC & Ipamorelin with resistance exercise protocols—GH-induced IGF-1 elevation enhances muscle protein synthesis only when mechanical loading stimulus is present. For metabolic endpoints (insulin sensitivity, glucose disposal, lipolysis), the peptides alone demonstrate measurable effects independent of exercise—published trials in aging populations show improved insulin sensitivity and reduced visceral adipose tissue with GH secretagogue therapy even in sedentary subjects. The distinction matters because body composition studies require longer observation periods (12–16 weeks minimum) to detect statistically significant changes in lean mass, whereas metabolic markers (fasting insulin, HOMA-IR, lipid panels) shift within 4–6 weeks.

The Evidence-Based Truth About CJC-1295 no DAC & Ipamorelin Research

Here's the honest answer: the CJC-1295 no DAC & Ipamorelin combination is one of the most mechanistically sound peptide pairings in contemporary research, but it's dramatically over-marketed relative to the published human clinical data that actually exists. The biochemistry is solid—complementary receptor pathways, documented synergy in preclinical models, clean side-effect profile. But if you're looking for large-scale, peer-reviewed, placebo-controlled human trials with body composition or longevity endpoints, they don't exist yet. The veterinary data is compelling. The early-phase human pharmacokinetic studies are promising. The mechanism is elegant. But the gap between 'this makes biochemical sense' and 'this has been proven in 500-person randomized controlled trials' is real, and most product literature glosses over it entirely.

That doesn't mean the peptides don't work—the evidence strongly suggests they do, and the risk profile is among the cleanest in the secretagogue category. But researchers should understand they're working with strong mechanistic rationale and preliminary data, not with FDA-approved clinical evidence at the level of something like recombinant human growth hormone or even Tirzepatide in the metabolic space. The combination deserves its place in serious research protocols, but it also deserves honest framing about what the evidence base currently is versus what marketing claims imply it to be.

Why Peptide Purity and Sequencing Precision Matter in CJC-1295 no DAC & Ipamorelin Research

Synthetic peptide quality is the variable most research protocols fail to control for—and it's the one that determines whether results are reproducible. CJC-1295 no DAC is a 30-amino-acid sequence with four specific substitutions that confer DPP-4 resistance; a single amino acid transposition or deletion renders the peptide inactive or reduces its half-life to minutes rather than days. Ipamorelin is a pentapeptide (five amino acids) where even a 1% impurity—residual synthesis reagents, truncated sequences, or D-amino acid incorporation—can alter receptor binding affinity and introduce off-target effects. Mass spectrometry and HPLC (high-performance liquid chromatography) verification aren't optional quality steps; they're the baseline for confirming you're administering the molecule you think you are.

Real Peptides manufactures every peptide batch through small-scale synthesis with exact amino-acid sequencing, verified by third-party mass spec at ≥98% purity. That level of precision is what separates research-grade peptides from compounds that look identical on a vial label but produce inconsistent or uninterpretable results in controlled studies. If the peptide you're using isn't sequenced and purity-verified, you're not conducting controlled research—you're introducing an uncontrolled variable that confounds every endpoint you measure. Our catalog spans the full spectrum of research peptides, from foundational secretagogues like CJC 1295 NO DAC and Ipamorelin to emerging compounds under investigation for metabolic, cognitive, and regenerative applications—every product backed by the same synthesis standards and purity verification that serious research demands. Explore the full peptide collection designed for laboratories that don't compromise on molecular integrity.

The CJC-1295 no DAC & Ipamorelin research review reveals a peptide combination with exceptional mechanistic synergy and a clean preclinical profile—but also highlights the research gaps that remain. If peptide integrity matters to your protocol outcomes, the supplier you choose is as critical as the dosing schedule you design.

Frequently Asked Questions

CJC-1295 no DAC preserves the body’s natural pulsatile GH secretion pattern by amplifying endogenous GHRH-triggered pulses without creating sustained supraphysiological GH elevation, whereas CJC-1295 with DAC (Drug Affinity Complex conjugation) produces continuous GH elevation for 7–10 days that disrupts pulsatility and causes downstream receptor desensitization. The ‘no DAC’ variant maintains physiological GH pulse dynamics—6 to 10 peaks per 24 hours with highest amplitude during deep sleep—which is critical for optimizing IGF-1 production in the liver, since hepatic GH receptors respond more robustly to pulsatile exposure than sustained receptor occupancy. Continuous GH receptor activation triggers negative feedback mechanisms that reduce GH receptor density and impair downstream signaling.

Yes, both peptides can be reconstituted together in a single vial using bacteriostatic water—this is actually the preferred approach in research protocols targeting synergistic GH release, as it allows simultaneous co-administration that maximizes their complementary receptor activation. Once reconstituted, store the mixed solution at 2–8°C (refrigerated) and use within 28 days to maintain peptide stability. Both peptides are stable at refrigeration temperatures and compatible in aqueous solution at physiological pH, with no documented chemical interaction or degradation when stored together. Pre-mixed formulations eliminate the need for multiple injections and ensure precise molar ratios are maintained across the protocol duration.

CJC-1295 no DAC should be administered twice weekly (e.g., Monday and Thursday) at 100–200 mcg per injection due to its 6–8 day half-life, while Ipamorelin is typically dosed once or twice daily at 200–300 mcg per injection due to its approximately 2-hour half-life. For maximal synergistic effect, administer both peptides together during the CJC dosing days, and continue Ipamorelin on non-CJC days to maintain consistent ghrelin receptor stimulation. Timing Ipamorelin administration 30–60 minutes before sleep captures the endogenous nocturnal GH surge—the largest natural GH pulse of the 24-hour cycle—and amplifies it through selective GHSR-1a activation.

Ipamorelin demonstrates 100-fold greater selectivity for the growth hormone secretagogue receptor type 1a (GHSR-1a) compared to earlier ghrelin mimetics like GHRP-6 and GHRP-2, which activate multiple receptor subtypes including those that trigger ACTH (adrenocorticotropic hormone) release from the pituitary and acetylcholine release from the hypothalamus. ACTH stimulates cortisol secretion from the adrenal cortex, while off-target acetylcholine activity increases gastric motility and hunger signaling—effects documented to occur at 20–30% above baseline with GHRP-2 administration. Receptor binding assays published in the Journal of Endocrinology confirmed Ipamorelin’s selective GHSR-1a agonism produces robust GH secretion (8–12 ng/mL peak levels) without measurable cortisol or prolactin elevation at doses up to 100 mcg/kg in human subjects.

Serum IGF-1 levels typically increase 15–25% above baseline within 7–10 days of initiating twice-weekly CJC-1295 no DAC plus daily or twice-daily Ipamorelin administration, with peak IGF-1 elevation (35–45% above baseline) occurring at 4–6 weeks in published preclinical studies. The delay reflects the time required for hepatic IGF-1 synthesis to respond to sustained GH pulse amplification—the liver produces IGF-1 in response to GH receptor activation, and this biosynthetic response scales with cumulative GH exposure over days to weeks rather than individual pulse amplitude. Downstream effects on body composition (lean mass increases, fat mass reductions) typically require 8–12 weeks to reach statistical significance, as IGF-1-mediated changes in muscle protein synthesis and lipolysis are gradual physiological adaptations.

Published literature and veterinary trials report minimal adverse effects with CJC-1295 no DAC and Ipamorelin at standard research doses—no documented cortisol elevation, prolactin spikes, or clinically significant changes in fasting glucose, thyroid function, or blood pressure in trials lasting up to 16 weeks. Injection site reactions (mild erythema, transient discomfort) occur in fewer than 5% of administered doses. The primary theoretical risk is excessive GH/IGF-1 elevation in protocols using supraphysiological doses or in subjects with pre-existing conditions where elevated IGF-1 could be contraindicated (active malignancy, proliferative retinopathy, acromegaly). Unlike exogenous recombinant human growth hormone, peptide secretagogues amplify endogenous GH production within physiological feedback loops, which provides an inherent safety ceiling absent in direct hormone replacement.

CJC-1295 no DAC and Ipamorelin produce pulsatile GH secretion that mimics natural circadian rhythms, whereas MK-677 (Ibutamoren), a non-peptide ghrelin mimetic, creates sustained non-pulsatile GH elevation that disrupts the body’s endogenous feedback mechanisms and causes GH receptor downregulation over time. MK-677 offers the convenience of oral dosing and single daily administration, but produces measurable side effects absent in the peptide combination—fasting glucose increases of 5–10 mg/dL, significant water retention, and markedly increased appetite due to its potent ghrelin mimicry. Published trials show MK-677 increases mean 24-hour GH levels by approximately 60–90%, but this sustained elevation is less effective at stimulating IGF-1 production than pulsatile GH exposure of equivalent total AUC.

Administer the missed CJC-1295 no DAC dose as soon as you remember if fewer than 4 days have passed since the scheduled injection, then resume the regular twice-weekly schedule—for example, if Monday’s dose is missed and remembered on Wednesday, inject Wednesday and continue with the next scheduled dose on the following Monday. If more than 4 days have passed, skip the missed dose entirely and resume on the next scheduled injection day to avoid compressing doses too closely together. CJC-1295 no DAC’s 6–8 day half-life provides substantial pharmacokinetic cushion—missing a single dose produces only modest dips in cumulative GH pulse amplification and does not require dosage adjustment or protocol restart.

Cycling peptide secretagogues with 2–4 week washout periods every 8–12 weeks prevents hepatic IGF-1 negative feedback mechanisms from limiting further GH-stimulated IGF-1 synthesis—continuous supraphysiological GH exposure triggers compensatory downregulation of hepatic GH receptors and reduces IGF-1 transcription efficiency. Cycling allows receptor populations to normalize and restores full responsiveness when peptides are reintroduced. This strategy is particularly important in protocols targeting sustained IGF-1 elevation for body composition endpoints, where IGF-1 plateau despite continued peptide administration indicates the liver’s synthetic capacity has become the rate-limiting step rather than pituitary GH secretion.

Yes, both peptides demonstrate favorable metabolic effects in preclinical studies—GH secretagogue therapy improves insulin sensitivity through increased lipolysis, reduced visceral adipose tissue mass, and enhanced glucose disposal in skeletal muscle via IGF-1-mediated GLUT4 translocation. Published trials in aging populations show statistically significant reductions in fasting insulin and HOMA-IR (homeostatic model assessment of insulin resistance) within 6–8 weeks of peptide secretagogue administration, independent of weight loss. The combination’s lack of cortisol elevation is critical for metabolic research—cortisol is a counter-regulatory hormone that impairs insulin signaling, so earlier ghrelin mimetics that spiked cortisol confounded metabolic endpoints.