Ipamorelin vs Macimorelin
A uniquely selective growth hormone booster that tells your pituitary to release more GH without messing with your cortisol or other hormones—making it the 'clean' choice among growth hormone peptides.
FDA-approved diagnostic test for adult growth hormone deficiency
Written by Michael Carroll — Owner, Director of Research · Reviewed by the Peptide Initiative Research Team · Editorial standards
Quick comparison
Dose range
Ipamorelin
200–200 mcg
Macimorelin
0.5–0.5 mg/kg
Frequency
Ipamorelin
Multiple times daily
Macimorelin
As needed
Administration
Ipamorelin
Subcutaneous injection
Macimorelin
Oral (reconstituted solution)
Cycle length
Ipamorelin
8-12 weeks
Macimorelin
4-6 weeks
Onset speed
Ipamorelin
Moderate (1-2 weeks)
Macimorelin
Rapid (hours to days)
Evidence level
Ipamorelin
Moderate human trials (Phase 1-2)
Macimorelin
Strong human trials (Phase 3 or FDA approved)
Benefit ratings
GH Selectivity
Recovery Support
Safety Profile
Diagnostic Accuracy
Safety & Tolerability
Convenience & Patient Experience
Compound specifications
Ipamorelin
Molecular formula
C38H49N9O5
Molecular weight
711.85 g/mol
Half-life
2 hours
Bioavailability
High when injected subcutaneously
CAS number
170851-70-4
Macimorelin
Molecular formula
C26H30N6O3
Molecular weight
474.6 g/mol
Half-life
4.1 hours
Bioavailability
Oral; food decreases Cmax and AUC by approximately 50-55% — must be administered fasting
CAS number
381231-18-1
Dosing compared
Ipamorelin
Subcutaneous
100 mcg per injection
2-3 times daily · 4-8 weeks
Conservative entry dose; Ipamorelin is a selective GH secretagogue with a ~2 hour half-life, so doses are split through the day [1][2]. Used in research and practice to assess tolerance before titrating up.
200 mcg per injection
2-3 times daily · 8-12 weeks
Most commonly cited research/practice dose; gives a meaningful pulsatile GH release without raising cortisol or prolactin at standard doses [1][2].
300 mcg per injection
3 times daily · 8-12 weeks
Upper end of the commonly used range; total daily exposure split across three injections. Used in practice by experienced users [1].
Macimorelin
Oral
0.5 mg/kg
Single dose · One-time diagnostic test
FDA-label (Macrilen) single oral dose for diagnosing adult growth hormone deficiency. Granules (60 mg) are reconstituted in 120 mL water (0.5 mg/mL) and taken after an 8-hour fast; serum GH below 2.8 ng/mL across the 30/45/60/90-minute draws confirms deficiency [4].
Best suited for
Ipamorelin
Clean GH Boost Seekers
If you want the benefits of increased growth hormone without spiking cortisol or other stress hormones, Ipamorelin is uniquely selective. Unlike GHRP-2 or GHRP-6, it won't raise your cortisol levels even at doses 200 times higher than needed for GH release.
Recovery-Focused Athletes
Ipamorelin shines for athletes who want better recovery between training sessions. The GH boost helps repair muscle tissue faster, and since it doesn't mess with other hormones, you can use it consistently without the rollercoaster effects.
Anti-Aging Enthusiasts
Growth hormone naturally declines as we age, contributing to muscle loss, fat gain, and reduced vitality. Ipamorelin offers a gentle way to restore more youthful GH levels without the risks of actual HGH therapy.
Those Recovering from Steroid Use
Research shows Ipamorelin can help counteract the muscle and bone-weakening effects of glucocorticoid medications. If you've been on steroids for medical reasons, this peptide may help you rebuild what you've lost.
Macimorelin
Diagnosis of Adult Growth Hormone Deficiency
Macimorelin is FDA-approved specifically for diagnosing AGHD in adults. It replaces the insulin tolerance test (ITT) as a safer, more convenient, and equally accurate diagnostic option. Phase 3 trials showed 87% sensitivity and 96% specificity.
Patients Intolerant or Contraindicated for ITT
For patients who cannot safely undergo insulin tolerance testing due to cardiac risk, seizure history, or other contraindications, macimorelin offers an evidence-based non-invasive alternative.
Clinical Confirmation Testing
With 97% reproducibility on retesting, macimorelin can reliably confirm GH deficiency diagnoses and monitor therapeutic responses over time with excellent consistency.
Side effects
Ipamorelin
Common
- Mild headache
- Injection site reactions
- Water retention
- Increased appetite
Uncommon
- Tingling in hands or feet
- Joint stiffness
Serious
- Allergic reaction
Macimorelin
Common
- Dysgeusia (abnormal taste)
- Dizziness
- Headache
- Fatigue
- Nausea
- Increased Appetite
Serious
- Cardiovascular events
Safety & evidence
Ipamorelin
Evidence level
Moderate human trials (Phase 1-2)
FDA status
Research compound
Safety overview
Ipamorelin's main selling point is that it raises growth hormone without raising cortisol or ACTH — two stress hormones that similar peptides do raise. That was shown in pigs, and it held even at doses more than 200 times higher than the amount needed to raise growth hormone [1]. It has not been checked in people. The two published human studies measured ipamorelin and growth hormone only; neither one assayed cortisol, ACTH or prolactin [2][3]. Most of what we know about safety in people comes from a single trial in patients recovering from bowel surgery. 114 people took part: 56 got ipamorelin through an IV for up to seven days, and 58 got a placebo. Most side effects were mild to moderate, and were the kind you would expect after surgery [3]. Serious problems happened at about the same rate in both groups — roughly 1 in 6 either way (17.9% on ipamorelin, 15.5% on placebo). But three things were more common on ipamorelin: low potassium in about 1 in 8 people versus about 1 in 30 on placebo (12.5% vs 3.4%), trouble sleeping in about 1 in 9 versus about 1 in 19 (10.7% vs 5.2%), and high blood sugar at discharge in about 1 in 7 versus about 1 in 12 (14.3% vs 8.6%) [6]. Two people taking ipamorelin died. Both had colon cancer surgery, and in both cases the surgical join in the bowel leaked afterward. Nobody on the placebo died. The FDA says it is unclear whether those deaths had anything to do with ipamorelin — but it pointed to them, along with the potassium and blood sugar differences, when it recommended in October 2024 against letting pharmacies compound ipamorelin [6].
Contraindications
- Active cancer or history of cancer
- Pregnancy or breastfeeding
- Pituitary disorders or tumors
- Known allergy to peptide components
- Children and adolescents (growth plates still open)
Macimorelin
Evidence level
Strong human trials (Phase 3 or FDA approved)
FDA status
FDA approved for this use
Safety overview
Macimorelin is well-tolerated with an excellent safety profile in clinical trials. No serious adverse events were reported in Phase 3 studies (n=154). Most side effects are mild and transient. QT prolongation of approximately 11 msec occurs but is generally not clinically significant. However, avoid combining with other QT-prolonging drugs.
Contraindications
- Patients with QT prolongation or QT/RR prolongation disorder
- Concurrent use with drugs known to prolong QT interval
- Patients with critical illness (acute medical or surgical illness)
- Known hypersensitivity to macimorelin or any components
- Patients unable to fast or follow fasting requirements
Which is right for you?
Choose Ipamorelin if...
- Muscle recovery and growth
- Anti-aging and vitality
- Body composition improvement
- Sleep quality enhancement
Choose Macimorelin if...
- Diagnosing adult growth hormone deficiency (AGHD)
- Patients who cannot tolerate or are contraindicated for insulin tolerance test
- Clinical settings requiring convenient, repeatable hormone testing
- Healthcare providers seeking FDA-approved diagnostic alternatives