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AI comparison summary

Biggest differences across Retatrutide · Tesamorelin · Thymosin Alpha-1

Focused on evidence grade, pharmacokinetics, and risks/interactions — with inline citations to the primary references on each peptide page.

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Retatrutide

Grade AMetabolic

Overview

Evidence grade: Grade A
Category: Metabolic
Primary focus: Triple GIP/GLP-1/glucagon agonist
Summary: Phase II trial results showed ~24% mean weight loss at 48 weeks at the 12 mg dose — markedly exceeding tirzepatide and prior GLP-1 monotherapies. Currently in Phase III; not yet FDA-approved but expected to be a landmark obesity and metabolic therapy.

Mechanism

Mechanism of action: First-in-class triple agonist of GIP, GLP-1, and glucagon receptors. The GLP-1 and GIP arms drive glucose-dependent insulin secretion and satiety; the glucagon arm increases energy expenditure — producing the largest weight-loss effect of any incretin to date.
Evidence explainer: Grade A — supported by multiple randomised human trials or an approved regulatory indication. Mechanism, dosing and safety are well characterised in humans.

Pharmacokinetics

Route: Subcutaneous injection
Half-life: ~6 days (supports once-weekly dosing)
PK notes: Retatrutide is administered subcutaneous injection with an approximate systemic half-life of ~6 days (supports once-weekly dosing). Steady-state and tissue-level effects can outlast plasma concentration, which is why dosing frequency (Once weekly) is designed to match receptor kinetics rather than plasma exposure. First-in-class triple agonist of GIP, GLP-1, and glucagon receptors. The GLP-1 and GIP arms drive glucose-dependent insulin secretion and satiety; the glucagon arm increases energy expenditure — producing the largest weight-loss effect of any incretin to date.

Administration

Typical dose: Titrated 2 mg → 4 mg → 8 mg → 12 mg
Frequency: Once weekly
Cycle length: Ongoing; weight regain occurs on cessation
Timing: Same day each week; any time of day
Protocol steps: Route: Subcutaneous injection. Typical starting dose Titrated 2 mg → 4 mg → 8 mg → 12 mg, Once weekly.
Timing: Same day each week; any time of day — keep it the same each dosing day to make effects legible.
Cycle length: Ongoing; weight regain occurs on cessation. Reassess with bloods and symptom logs before repeating.
Rotate sites across the abdomen (avoiding a 2 cm radius around the navel), outer thighs and flanks. Never inject through a bruise or mole.

Benefits

Reported benefits: ~24% mean weight loss at 48 weeks (Phase II)
Marked improvements in HbA1c, blood pressure, ApoB and liver fat
Convenient once-weekly dosing
Likely best-in-class cardiometabolic profile
Common stacks: Creatine monohydrate, Whey protein, Vitamin D3 + K2

Risks

Side effects: Nausea, vomiting, diarrhea (especially during titration)
Injection site reactions
Reduced appetite to the point of inadequate protein intake — pair with resistance training and protein targeting
Theoretical pancreatitis and gallbladder risk (class effect)
Contraindications: Personal or family history of medullary thyroid carcinoma
Multiple Endocrine Neoplasia type 2
Pregnancy and lactation
Prior severe reaction to GLP-1 agonists
Interactions: Insulin and sulfonylureas — Risk of hypoglycemia — dose reduction usually required.
Oral medications — Delayed gastric emptying may alter absorption; separate timing for narrow-therapeutic-index drugs.
Legal status: Investigational; not yet FDA-approved. Currently available only via clinical trials.

Tesamorelin

Grade AGrowth Hormone

Overview

Evidence grade: Grade A
Category: Growth Hormone
Primary focus: Visceral fat, growth hormone axis
Summary: The most rigorously evidenced peptide on this site, and the only one here approved by a major regulator. FDA-approved in 2010 as Egrifta for excess abdominal fat in HIV-associated lipodystrophy, on the back of phase 3 trials showing a 15-18% reduction in visceral adipose tissue against placebo. Everything outside that indication — the anti-ageing and body-composition uses it is sold for — is extrapolation from a population that is not you.

Mechanism

Mechanism of action: A synthetic analogue of the full 44-amino-acid human growth hormone releasing factor, with a hexenoyl group on the N-terminus that slows enzymatic degradation. It binds pituitary GHRH receptors to restore pulsatile growth hormone secretion, raising IGF-1 and shifting adipose metabolism preferentially against visceral rather than subcutaneous fat.
Evidence explainer: Grade A — supported by multiple randomised human trials or an approved regulatory indication. Mechanism, dosing and safety are well characterised in humans.

Pharmacokinetics

Route: Subcutaneous injection
Half-life: ~26 minutes in plasma; the growth hormone rise it triggers persists 4-6 hours
PK notes: Tesamorelin is administered subcutaneous injection with an approximate systemic half-life of ~26 minutes in plasma; the growth hormone rise it triggers persists 4-6 hours. Steady-state and tissue-level effects can outlast plasma concentration, which is why dosing frequency (Once daily) is designed to match receptor kinetics rather than plasma exposure. A synthetic analogue of the full 44-amino-acid human growth hormone releasing factor, with a hexenoyl group on the N-terminus that slows enzymatic degradation. It binds pituitary GHRH receptors to restore pulsatile growth hormone secretion, raising IGF-1 and shifting adipose metabolism preferentially against visceral rather than subcutaneous fat.

Administration

Typical dose: 2 mg (1.28 mg for the newer F8/WR formulation)
Frequency: Once daily
Cycle length: 26 weeks in the pivotal trials; benefit reverses on stopping
Timing: Bedtime, to sit with the natural overnight GH pulse
Protocol steps: Route: Subcutaneous injection. Typical starting dose 2 mg (1.28 mg for the newer F8/WR formulation), Once daily.
Timing: Bedtime, to sit with the natural overnight GH pulse — keep it the same each dosing day to make effects legible.
Cycle length: 26 weeks in the pivotal trials; benefit reverses on stopping. Reassess with bloods and symptom logs before repeating.
Rotate sites across the abdomen (avoiding a 2 cm radius around the navel), outer thighs and flanks. Never inject through a bruise or mole.

Benefits

Reported benefits: 15-18% reduction in visceral adipose tissue versus placebo in phase 3 trials
Improved triglycerides and cholesterol alongside the fat loss
Raises IGF-1 without the supraphysiological spikes of exogenous growth hormone
Does not reduce subcutaneous fat, which is metabolically less harmful
Common stacks: Zone 2 cardio, Resistance training, Regular HbA1c and IGF-1 monitoring

Risks

Side effects: Injection site reactions, the commonest complaint in trials
Joint pain and peripheral oedema, both dose-related and GH-mediated
Raised blood glucose and reduced insulin sensitivity — monitor if prediabetic
Carpal tunnel symptoms at higher exposures
Contraindications: Active malignancy — growth hormone is mitogenic and IGF-1 is a growth signal
Pituitary disease, pituitary surgery or head irradiation
Pregnancy and lactation
Diabetic retinopathy
Interactions: Insulin and sulfonylureas — Tesamorelin worsens insulin sensitivity; glycaemic control may need adjusting.
Corticosteroids — Blunt the GH response and add their own metabolic burden.
GHRH analogues (CJC-1295) — Same receptor. Stacking adds risk, not effect.
Legal status: FDA-approved as Egrifta and Egrifta SV/WR for HIV-associated lipodystrophy only, and prescription-only. Use for body composition or anti-ageing is off-label. Material sold online as research-grade tesamorelin is not the approved product and carries no purity guarantee.

Thymosin Alpha-1

Grade BLongevity

Overview

Evidence grade: Grade B
Category: Longevity
Primary focus: Immune modulation
Summary: Approved as Zadaxin in more than 35 countries for chronic hepatitis B, though not by the FDA. The evidence base is genuinely substantial by peptide standards — a meta-analysis of sepsis trials covering nearly 2,000 patients found a reduction in 28-day mortality. The longevity rationale rests on thymic involution, the well-documented shrinking of the thymus with age, but no trial has tested whether it slows ageing in healthy adults.

Mechanism

Mechanism of action: A 28-amino-acid peptide produced naturally by the thymus. It signals through toll-like receptor 9 on dendritic cells, pushing differentiation toward a Th1 response, supporting T-cell maturation and normalising cytokine output. It modulates an immune system rather than simply stimulating one, which is why it has been trialled in both immunosuppression and inflammation.
Evidence explainer: Grade B — supported by preclinical evidence plus at least one small human trial, pharmacokinetic study, or strong translational rationale. Human long-term safety is incomplete.

Pharmacokinetics

Route: Subcutaneous injection
Half-life: Roughly 2 hours. The 25-hour figure widely quoted online is for an engineered Fc-fusion variant used in research, not the peptide sold as Tα1.
PK notes: Thymosin Alpha-1 is administered subcutaneous injection with an approximate systemic half-life of Roughly 2 hours. The 25-hour figure widely quoted online is for an engineered Fc-fusion variant used in research, not the peptide sold as Tα1.. Steady-state and tissue-level effects can outlast plasma concentration, which is why dosing frequency (Twice weekly) is designed to match receptor kinetics rather than plasma exposure. A 28-amino-acid peptide produced naturally by the thymus. It signals through toll-like receptor 9 on dendritic cells, pushing differentiation toward a Th1 response, supporting T-cell maturation and normalising cytokine output. It modulates an immune system rather than simply stimulating one, which is why it has been trialled in both immunosuppression and inflammation.

Administration

Typical dose: 1.6 mg
Frequency: Twice weekly
Cycle length: 6-12 months in the hepatitis trials
Timing: Any time of day; consistency matters more than timing
Protocol steps: Route: Subcutaneous injection. Typical starting dose 1.6 mg, Twice weekly.
Timing: Any time of day; consistency matters more than timing — keep it the same each dosing day to make effects legible.
Cycle length: 6-12 months in the hepatitis trials. Reassess with bloods and symptom logs before repeating.
Rotate sites across the abdomen (avoiding a 2 cm radius around the navel), outer thighs and flanks. Never inject through a bruise or mole.

Benefits

Reported benefits: Reduced 28-day mortality in a meta-analysis of sepsis trials (RR 0.77)
40.6% versus 9.4% complete virological response in the pivotal hepatitis B trial
Restores T-cell counts and function in immunosuppressed patients
Well tolerated across long treatment courses
Common stacks: Vitamin D3 sufficiency, Zinc, Adequate sleep

Risks

Side effects: Injection site discomfort, the most common finding in trials
Transient fatigue in the first days of a course
Rare hypersensitivity reactions
Contraindications: Autoimmune disease — pushing a Th1 response may worsen it
Organ transplant recipients on immunosuppression
Pregnancy and lactation
Interactions: Immunosuppressants — Directly opposing mechanisms — do not combine without specialist advice.
Corticosteroids — Blunt the immune effect this peptide is taken for.
Legal status: Approved as Zadaxin in over 35 countries for chronic hepatitis B; not FDA-approved in the United States, where the FDA has moved thymosin alpha-1 to the category of substances that cannot be compounded. Research-grade material is unverified for purity or identity.

Attribute	Retatrutide Grade AMetabolic	Tesamorelin Grade AGrowth Hormone	Thymosin Alpha-1 Grade BLongevity
Overview
Evidence grade	Grade A	Grade A	Grade B
Category	Metabolic	Growth Hormone	Longevity
Primary focus	Triple GIP/GLP-1/glucagon agonist	Visceral fat, growth hormone axis	Immune modulation
Summary	Phase II trial results showed ~24% mean weight loss at 48 weeks at the 12 mg dose — markedly exceeding tirzepatide and prior GLP-1 monotherapies. Currently in Phase III; not yet FDA-approved but expected to be a landmark obesity and metabolic therapy.	The most rigorously evidenced peptide on this site, and the only one here approved by a major regulator. FDA-approved in 2010 as Egrifta for excess abdominal fat in HIV-associated lipodystrophy, on the back of phase 3 trials showing a 15-18% reduction in visceral adipose tissue against placebo. Everything outside that indication — the anti-ageing and body-composition uses it is sold for — is extrapolation from a population that is not you.	Approved as Zadaxin in more than 35 countries for chronic hepatitis B, though not by the FDA. The evidence base is genuinely substantial by peptide standards — a meta-analysis of sepsis trials covering nearly 2,000 patients found a reduction in 28-day mortality. The longevity rationale rests on thymic involution, the well-documented shrinking of the thymus with age, but no trial has tested whether it slows ageing in healthy adults.
Mechanism
Mechanism of action	First-in-class triple agonist of GIP, GLP-1, and glucagon receptors. The GLP-1 and GIP arms drive glucose-dependent insulin secretion and satiety; the glucagon arm increases energy expenditure — producing the largest weight-loss effect of any incretin to date.	A synthetic analogue of the full 44-amino-acid human growth hormone releasing factor, with a hexenoyl group on the N-terminus that slows enzymatic degradation. It binds pituitary GHRH receptors to restore pulsatile growth hormone secretion, raising IGF-1 and shifting adipose metabolism preferentially against visceral rather than subcutaneous fat.	A 28-amino-acid peptide produced naturally by the thymus. It signals through toll-like receptor 9 on dendritic cells, pushing differentiation toward a Th1 response, supporting T-cell maturation and normalising cytokine output. It modulates an immune system rather than simply stimulating one, which is why it has been trialled in both immunosuppression and inflammation.
Evidence explainer	Grade A — supported by multiple randomised human trials or an approved regulatory indication. Mechanism, dosing and safety are well characterised in humans.	Grade A — supported by multiple randomised human trials or an approved regulatory indication. Mechanism, dosing and safety are well characterised in humans.	Grade B — supported by preclinical evidence plus at least one small human trial, pharmacokinetic study, or strong translational rationale. Human long-term safety is incomplete.
Pharmacokinetics
Route	Subcutaneous injection	Subcutaneous injection	Subcutaneous injection
Half-life	~6 days (supports once-weekly dosing)	~26 minutes in plasma; the growth hormone rise it triggers persists 4-6 hours	Roughly 2 hours. The 25-hour figure widely quoted online is for an engineered Fc-fusion variant used in research, not the peptide sold as Tα1.
PK notes	Retatrutide is administered subcutaneous injection with an approximate systemic half-life of ~6 days (supports once-weekly dosing). Steady-state and tissue-level effects can outlast plasma concentration, which is why dosing frequency (Once weekly) is designed to match receptor kinetics rather than plasma exposure. First-in-class triple agonist of GIP, GLP-1, and glucagon receptors. The GLP-1 and GIP arms drive glucose-dependent insulin secretion and satiety; the glucagon arm increases energy expenditure — producing the largest weight-loss effect of any incretin to date.	Tesamorelin is administered subcutaneous injection with an approximate systemic half-life of ~26 minutes in plasma; the growth hormone rise it triggers persists 4-6 hours. Steady-state and tissue-level effects can outlast plasma concentration, which is why dosing frequency (Once daily) is designed to match receptor kinetics rather than plasma exposure. A synthetic analogue of the full 44-amino-acid human growth hormone releasing factor, with a hexenoyl group on the N-terminus that slows enzymatic degradation. It binds pituitary GHRH receptors to restore pulsatile growth hormone secretion, raising IGF-1 and shifting adipose metabolism preferentially against visceral rather than subcutaneous fat.	Thymosin Alpha-1 is administered subcutaneous injection with an approximate systemic half-life of Roughly 2 hours. The 25-hour figure widely quoted online is for an engineered Fc-fusion variant used in research, not the peptide sold as Tα1.. Steady-state and tissue-level effects can outlast plasma concentration, which is why dosing frequency (Twice weekly) is designed to match receptor kinetics rather than plasma exposure. A 28-amino-acid peptide produced naturally by the thymus. It signals through toll-like receptor 9 on dendritic cells, pushing differentiation toward a Th1 response, supporting T-cell maturation and normalising cytokine output. It modulates an immune system rather than simply stimulating one, which is why it has been trialled in both immunosuppression and inflammation.
Administration
Typical dose	Titrated 2 mg → 4 mg → 8 mg → 12 mg	2 mg (1.28 mg for the newer F8/WR formulation)	1.6 mg
Frequency	Once weekly	Once daily	Twice weekly
Cycle length	Ongoing; weight regain occurs on cessation	26 weeks in the pivotal trials; benefit reverses on stopping	6-12 months in the hepatitis trials
Timing	Same day each week; any time of day	Bedtime, to sit with the natural overnight GH pulse	Any time of day; consistency matters more than timing
Protocol steps	Route: Subcutaneous injection. Typical starting dose Titrated 2 mg → 4 mg → 8 mg → 12 mg, Once weekly. Timing: Same day each week; any time of day — keep it the same each dosing day to make effects legible. Cycle length: Ongoing; weight regain occurs on cessation. Reassess with bloods and symptom logs before repeating. Rotate sites across the abdomen (avoiding a 2 cm radius around the navel), outer thighs and flanks. Never inject through a bruise or mole.	Route: Subcutaneous injection. Typical starting dose 2 mg (1.28 mg for the newer F8/WR formulation), Once daily. Timing: Bedtime, to sit with the natural overnight GH pulse — keep it the same each dosing day to make effects legible. Cycle length: 26 weeks in the pivotal trials; benefit reverses on stopping. Reassess with bloods and symptom logs before repeating. Rotate sites across the abdomen (avoiding a 2 cm radius around the navel), outer thighs and flanks. Never inject through a bruise or mole.	Route: Subcutaneous injection. Typical starting dose 1.6 mg, Twice weekly. Timing: Any time of day; consistency matters more than timing — keep it the same each dosing day to make effects legible. Cycle length: 6-12 months in the hepatitis trials. Reassess with bloods and symptom logs before repeating. Rotate sites across the abdomen (avoiding a 2 cm radius around the navel), outer thighs and flanks. Never inject through a bruise or mole.
Benefits
Reported benefits	~24% mean weight loss at 48 weeks (Phase II) Marked improvements in HbA1c, blood pressure, ApoB and liver fat Convenient once-weekly dosing Likely best-in-class cardiometabolic profile	15-18% reduction in visceral adipose tissue versus placebo in phase 3 trials Improved triglycerides and cholesterol alongside the fat loss Raises IGF-1 without the supraphysiological spikes of exogenous growth hormone Does not reduce subcutaneous fat, which is metabolically less harmful	Reduced 28-day mortality in a meta-analysis of sepsis trials (RR 0.77) 40.6% versus 9.4% complete virological response in the pivotal hepatitis B trial Restores T-cell counts and function in immunosuppressed patients Well tolerated across long treatment courses
Common stacks	Creatine monohydrate, Whey protein, Vitamin D3 + K2	Zone 2 cardio, Resistance training, Regular HbA1c and IGF-1 monitoring	Vitamin D3 sufficiency, Zinc, Adequate sleep
Risks
Side effects	Nausea, vomiting, diarrhea (especially during titration) Injection site reactions Reduced appetite to the point of inadequate protein intake — pair with resistance training and protein targeting Theoretical pancreatitis and gallbladder risk (class effect)	Injection site reactions, the commonest complaint in trials Joint pain and peripheral oedema, both dose-related and GH-mediated Raised blood glucose and reduced insulin sensitivity — monitor if prediabetic Carpal tunnel symptoms at higher exposures	Injection site discomfort, the most common finding in trials Transient fatigue in the first days of a course Rare hypersensitivity reactions
Contraindications	Personal or family history of medullary thyroid carcinoma Multiple Endocrine Neoplasia type 2 Pregnancy and lactation Prior severe reaction to GLP-1 agonists	Active malignancy — growth hormone is mitogenic and IGF-1 is a growth signal Pituitary disease, pituitary surgery or head irradiation Pregnancy and lactation Diabetic retinopathy	Autoimmune disease — pushing a Th1 response may worsen it Organ transplant recipients on immunosuppression Pregnancy and lactation
Interactions	Insulin and sulfonylureas — Risk of hypoglycemia — dose reduction usually required. Oral medications — Delayed gastric emptying may alter absorption; separate timing for narrow-therapeutic-index drugs.	Insulin and sulfonylureas — Tesamorelin worsens insulin sensitivity; glycaemic control may need adjusting. Corticosteroids — Blunt the GH response and add their own metabolic burden. GHRH analogues (CJC-1295) — Same receptor. Stacking adds risk, not effect.	Immunosuppressants — Directly opposing mechanisms — do not combine without specialist advice. Corticosteroids — Blunt the immune effect this peptide is taken for.
Legal status	Investigational; not yet FDA-approved. Currently available only via clinical trials.	FDA-approved as Egrifta and Egrifta SV/WR for HIV-associated lipodystrophy only, and prescription-only. Use for body composition or anti-ageing is off-label. Material sold online as research-grade tesamorelin is not the approved product and carries no purity guarantee.	Approved as Zadaxin in over 35 countries for chronic hepatitis B; not FDA-approved in the United States, where the FDA has moved thymosin alpha-1 to the category of substances that cannot be compounded. Research-grade material is unverified for purity or identity.

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