What Is Ipamorelin and Why Is It the Most Popular GHRP?
Ipamorelin is a pentapeptide (Aib-His-D-2Nal-D-Phe-Lys-NH2) that selectively activates the growth hormone secretagogue receptor (GHS-R1a), also known as the ghrelin receptor. It is classified as a growth hormone releasing peptide (GHRP) — the class of peptides that triggers GH release from the anterior pituitary.
The word "selective" is doing enormous work in that sentence. Every GHRP activates GHS-R1a and stimulates GH release. But most GHRPs also stimulate cortisol and prolactin release — two hormones you absolutely do not want chronically elevated. GHRP-6 increases cortisol by approximately 36% at therapeutic doses. GHRP-2 increases cortisol by approximately 20%. Hexarelin, the most potent GHRP, significantly elevates both cortisol and prolactin. Ipamorelin does neither. In the definitive selectivity study (Raun et al., Eur J Endocrinol 1998), ipamorelin produced dose-dependent GH release without any statistically significant change in cortisol, prolactin, FSH, LH, or TSH at any dose tested — including supratherapeutic doses up to 1 mg/kg.
This selectivity profile is why ipamorelin has become the default GHRP recommendation in the peptide optimization community. It provides the GH stimulus without the hormonal baggage.
Understanding the Saturation Dose
The "saturation dose" is the most important concept in GHRP dosing. It refers to the dose at which the GHS-R1a receptor population is fully occupied — meaning additional peptide will not produce additional GH release. For GHRPs, this saturation dose is approximately 1 mcg per kg of body weight.
For an 80 kg (176 lb) person, the saturation dose is approximately 80 mcg. For a 100 kg (220 lb) person, approximately 100 mcg. Importantly, going above the saturation dose does not increase GH output — the receptors are already fully occupied. Some researchers use doses up to 200-300 mcg per injection, but the additional peptide above saturation is pharmacologically inactive. It does not cause harm, but it wastes product.
This has practical implications for your dosing: if you weigh 80 kg, a 200 mcg dose delivers no more GH than a 100 mcg dose. You are using twice the product for zero additional benefit. Calculate your saturation dose (body weight in kg × 1 mcg/kg) and dose at or slightly above that threshold.
Optimal Timing: Why Fasting Matters
Ipamorelin should be injected on an empty stomach — ideally after a minimum 1-hour fast, preferably 2 hours. Do not eat for at least 30 minutes after injection. This is not optional guidance; fasting is mechanistically critical for maximum GH pulse amplitude.
The reason is insulin. Insulin is a potent suppressor of GH release. When you eat — particularly carbohydrates and protein — insulin rises within 15-30 minutes. Elevated insulin directly inhibits GH release from the pituitary via IGF-1 negative feedback and by reducing GH mRNA expression. Studies measuring GH response to GHRP stimulation in fed vs fasted states show a 40-60% reduction in peak GH when insulin is elevated.
The three optimal injection windows are: (1) 30-60 minutes before bed (most important — aligns with nocturnal GH pulse); (2) immediately upon waking (before breakfast); (3) 30 minutes before a workout (on an empty stomach). Most users inject once daily (before bed). Advanced protocols use 2-3 injections daily at all three windows.
Stacking Ipamorelin with CJC-1295 (No DAC)
The ipamorelin + CJC-1295 (no DAC) stack is the gold standard GH secretagogue protocol. The synergy is not additive — it is multiplicative. GHRP (ipamorelin) triggers GH release by activating GHS-R1a. GHRH analog (CJC-1295 no DAC) amplifies GH pulse amplitude by activating the GHRH receptor on the same somatotroph cells. When both receptors are activated simultaneously, the GH output is significantly greater than the sum of either peptide alone.
The biological basis for this synergy is well-established. GHRH and GHRP act through different intracellular signaling pathways that converge on GH vesicle exocytosis. GHRH activates the cAMP/PKA pathway. GHRP activates the PKC/IP3 pathway. The combination produces maximal GH vesicle release through dual-pathway activation — a concept sometimes called "full-axis engagement."
Standard stack dosing: 100-200 mcg ipamorelin + 100-200 mcg CJC-1295 no DAC, mixed in the same syringe, injected subcutaneously 30-60 minutes before bed. The CalcMyPeptide blend/stack calculator handles the math for drawing from two separate vials into one syringe.
Reconstitution and Practical Dosing Math
Ipamorelin typically comes in 2 mg or 5 mg lyophilized vials. For a 5 mg vial reconstituted with 2.5 mL bacteriostatic water: concentration = 5,000 mcg / 2.5 mL = 2,000 mcg/mL. On a U-100 insulin syringe (100 units = 1 mL): each unit = 20 mcg. For a 200 mcg dose, draw 10 units. For a 100 mcg (saturation dose) for a 100 kg person, draw 5 units.
For a 2 mg vial with 1 mL BAC water: concentration = 2,000 mcg/mL. Same math — 10 units = 200 mcg. The 2 mg vials are less economical per dose but useful if you are testing ipamorelin for the first time and don't want to commit to a full 5 mg vial.
Storage after reconstitution: refrigerate at 2-8°C (36-46°F), use within 28 days. Do not freeze reconstituted solution. Label the vial with the reconstitution date immediately. Use the CalcMyPeptide reconstitution calculator to confirm your exact draw volume — reconstitution math errors are the most common dosing mistake in the peptide community.