This article summarizes published peptide research. All content is presented for research reference only and is not intended as medical advice or guidance for personal peptide use. Products referenced are research compounds — not for human consumption, diagnostic or therapeutic application.

Weight-loss peptides are the fastest-growing category in modern obesity pharmacology. Over the past five years the GLP-1 agonist class and its dual and triple analogues have completely reshaped what is achievable without bariatric surgery. Semaglutide, tirzepatide, retatrutide and cagrilintide show 15-metabolic changes over 68-72 weeks in clinical trials — a result that seemed impossible a decade ago. This guide walks through the molecule hierarchy, real SURMOUNT-1, STEP-1 and retatrutide phase-2 data, titration protocols, side-effect mitigation, muscle and skin preservation, stacks with ipamorelin, GHK-Cu, AOD-9604 and MOTS-C, plus myths, FAQ and concrete recommendations by goal type.

What GLP-1 peptides are and why they work

GLP-1 (glucagon-like peptide 1) is an incretin hormone released by intestinal L-cells in response to food. Modern analogues mimic it with a modified structure resistant to DPP-4, extending half-life from 2 minutes (native) to 5-7 days PubMed 31705817. Weight loss is delivered through three mechanisms. First, central appetite suppression via hypothalamic and brainstem GLP-1 receptors PubMed 26284720. Second, slowed gastric emptying, extending fullness by 2-4 hours. Third, improved insulin sensitivity and glucose-dependent insulin release. Net behavioural effect: spontaneous 500-700 kcal/day reduction without willpower. Bonus: semaglutide reduced major cardiovascular events by 20% in large outcome trials PubMed 34506739. See GLP-1 for longevity.

GLP-1 hierarchy by effect size

Class	Molecule	Receptors	Peak loss	Horizon
Mono	Semaglutide	GLP-1	14.9%	68 weeks
Mono (older)	Liraglutide	GLP-1	7-8%	56 weeks
Dual	Tirzepatide	GLP-1 + GIP	20.9%	72 weeks
Triple	Retatrutide	GLP-1 + GIP + Glucagon	24.2%	48 weeks
Amylin	Cagrilintide	Amylin	10.8% mono	26 weeks
Dual amylin + GLP-1	Cagrisema	GLP-1 + Amylin	15.6-22.7%	68 weeks

Deeper pairwise comparisons in Tirzepatide vs Retatrutide, Cagrilintide vs Tirzepatide and Cagrilintide vs Mazdutide.

Semaglutide — the classic GLP-1

Semaglutide (Ozempic for type-2 diabetes, Wegovy for obesity) was the first GLP-1 to go mainstream. STEP-1 (Wilding 2021, n=1961, BMI >30 without diabetes) showed metabolic changes on 2.4 mg/wk vs 2.4% placebo PubMed 33567185. STEP-5 confirmed durability to 104 weeks PubMed 34706206, and STEP-8 showed near-double the effect of liraglutide PubMed 34706207. Standard titration: 0.25 → 0.5 → 1 → 1.7 → 2.4 mg, four weeks per step. Predictable, well-studied, but lower ceiling — 30-40% plateau at 10-12% by week 40.

Tirzepatide — dual agonist king

Tirzepatide (Mounjaro, Zepbound) is the first clinically registered GIP/GLP-1 co-agonist. Added GIP activity delivers +5-7% more loss than pure GLP-1 via enhanced thermogenesis and adipose lipolysis. SURMOUNT-1 (Jastreboff 2022, n=2539) showed 20.9% loss at 72 weeks on 15 mg vs 3.1% placebo PubMed 35658024, with 57% of patients losing >20% and 36% >25%. See AOD-9604 vs Tirzepatide.

Titration schedule

Weeks	Dose	Cumulative loss	Typical feel
1-4	2.5 mg	1-3 kg	Mild nausea days 1-3, appetite drop from day 5
5-8	5 mg	3-6 kg	Stable small-portion satiety
9-12	7.5 mg	6-10 kg	New food habits forming
13-16	10 mg	10-13 kg	Visible body-comp change
17-20	12.5 mg	13-16 kg	Pace slows but continues
21-72	15 mg	16-25 kg	Plateau, nutrition and training tune-up

When NOT to raise the dose

If nausea is marked, hold the step 6-8 weeks instead of 4. Many see 5 mg results equal to 10 mg — max dose isn't always needed. Raise only if side effects are minimal and loss slows below 0.3 kg/week.

Where and when to inject

Subcutaneous abdomen, thigh or upper arm, once weekly, same day. Morning before food is ideal. Pens dose precisely and painlessly — see PEPTEX pens.

Retatrutide — triple-agonist record holder

Retatrutide is the first molecule to activate GLP-1, GIP and glucagon. The glucagon arm lifts energy expenditure 10-15% via brown-fat and hepatic thermogenesis. Phase 2 (Jastreboff 2023, n=338) showed 24.2% loss at 48 weeks on 12 mg PubMed 37366315. Glucagon activity can transiently raise glucose — monitor 6-8 weeks. Ret + MOTS-C + NAD+ stack is detailed in Retatrutide stack.

Cagrilintide — amylin analogue for stacking

Cagrilintide is a long-acting amylin analogue signalling via area postrema — a separate satiety pathway from GLP-1. Phase 2 showed 10.8% mono-loss at 26 weeks PubMed 33795247; combined with semaglutide it hit 15.6-17.1% at 32 weeks PubMed 35939312. Full review: Cagrilintide amylin analogue.

AOD-9604 and MOTS-C — non-GLP-1 alternatives

Not everyone is a GLP-1 candidate. For contraindications (pancreatitis, MEN2, intolerance) or pure fat-loss without appetite suppression, alternatives exist. AOD-9604 is a GH fragment 176-191 stimulating lipolysis without IGF-1 impact PubMed 11602048; modest 3-5% over 12 weeks — see AOD-9604 honest review. MOTS-C is a mitochondrial peptide activating AMPK PubMed 25738459 — see MOTS-C and AMPK and MOTS-C mitochondrial peptide. 5-Amino-1-MQ vs AOD-9604 comparison — here. Full non-GLP-1 roundup: Peptides for fat burning.

Comparison table

Peptide	Frequency	Weight loss	Muscle / skin	Nausea risk	Best for
Semaglutide	1×/week	14-17%	Moderate losses	Medium	Beginners, BMI 27-32
Tirzepatide	1×/week	20-22%	Moderate losses	Medium	Most, BMI 30-40
Retatrutide	1×/week	24-27%	Higher at fast pace	High	Severe obesity, BMI >35
Cagrilintide	1×/week	10-11%	Minimal	Low	Soft start, stacking
AOD-9604	5×/week	3-5%	None	None	Localised fat, support
MOTS-C	2-3×/week	Metabolic	None	None	Insulin resistance

Week-by-week expectations

Weeks	Dose	Weight	Loss	Key focus
0	—	95.0 kg	—	Baseline BMI, waist, fasting glucose
4	2.5 mg	93.0	2 kg	Nausea settles, appetite stable
12	7.5 mg	88.5	6.5 kg	Add strength 2-3×/wk
24	12.5 mg	82.0	13 kg	Protein 1.8 g/kg, check hair/skin
48	15 mg	76.0	19 kg	Add ipamorelin + GHK-Cu if needed
72	15 mg	74.5	20.5 kg	Transition to maintenance dose

Side effects and m...