Macimorelin (Macrilen)_Dosage, benefits & legal status
Also known as Macrilen, AEZS-130, macimorelin acetate
An FDA-approved ghrelin agonist, and it is a diagnostic test rather than a treatment.
Common vial size is what vendors typically sell, not a recommendation. Enter your own vial in the calculator.
What is Macimorelin (Macrilen)?
Plain language first. The technical label stays, but it never stands alone.Overview
The one ghrelin drug the FDA approved, and it is a one-off test rather than a treatment. It replaced an older test that worked by deliberately crashing your blood sugar.
Macimorelin acetate, an orally active growth hormone secretagogue receptor agonist, FDA-approved in December 2017 as an oral diagnostic test for adult growth hormone deficiency. Administered as a single 0.5 mg/kg reconstituted oral solution after at least eight hours fasting, with timed post-dose growth hormone sampling. Strong CYP3A4 inducers may produce false positive results.
What it's used for
A single-dose oral test for diagnosing adult growth hormone deficiency.
How does Macimorelin (Macrilen) work?
What it does in the body, and where.Macimorelin is the answer to a question people ask about the GHRP family: has any of this been approved for anything.
- 01It provokes a growth hormone pulse on purposeAs a ghrelin receptor agonist it triggers the pituitary to release growth hormone. Blood samples taken afterwards show whether the gland can respond.
- 02It replaced an unpleasant older testThe insulin tolerance test was the reference standard, and it works by deliberately inducing low blood sugar under supervision. It is contraindicated in people with heart disease or seizure disorders. An oral alternative with comparable accuracy is a real improvement.
- 03One dose, onceThe label specifies a single oral dose of 0.5 mg per kilogram as a reconstituted solution after at least eight hours fasting. There is no repeat schedule because it is not a therapy.
- 04Drug interactions can produce a false resultThe label warns that strong CYP3A4 inducers can lower macimorelin levels and cause false positives, and that drugs affecting growth hormone secretion should be avoided around the test.
What else is it used for?
Each use below carries its own evidence level. Approved means regulators have cleared it for that purpose. Investigational means it is in trials. Early research means it is being studied and is not established.
- Diagnosis of adult growth hormone deficiencyFDA-approved
- Raising growth hormone as a treatment, which is not what it is approved fornone
How much, and do you cycle it?
The range, and whether you take breaks.0.5 mg per kg, once, single dose for the test. Set by the prescriptionFDA label
This is a prescription drug. Duration and schedule are set by the label and the prescriber, not by a cycling convention.
How long does it stay in the body?
The half-life, and where the figure comes from.Characterised in the FDA labelFDA label
Pharmacokinetics are described in the approved prescribing information. The test protocol depends on timed blood sampling after the single dose.
You can compare this against the whole library to see where it sits.
What does it cost?
Typical dose and cost, in plain numbers.Macimorelin (Macrilen) is not injected
It is taken by mouth (oral). A single oral dose of 0.5 mg per kilogram, given as a reconstituted solution after at least eight hours fasting. This is a diagnostic dose, not a treatment dose.
How do you store it?
Before mixing, and after.Room temperature. Cool, dry, out of light.
Macimorelin (Macrilen) is taken as a pill or capsule. Keep it in its original container at room temperature, away from heat, humidity, and direct sun. No fridge or mixing needed. Check the expiration date on the bottle.
What are the side effects and cautions?
Known cautions and warnings for this compound.Who should avoid it
- Pregnancy or breastfeeding, where the test has not been established
- Use as a growth hormone treatment, which is not an approved use
- Taking strong CYP3A4 inducers, which the label says should be stopped before the test
Stop and get help
- Signs of an allergic reaction, including facial or throat swelling or trouble breathing
- Palpitations or an irregular heartbeat
Common effects
- A temporary metallic or bitter taste, reported in the trials
- Headache
- Tiredness
- Nausea
Where this page says nothing is established, that means nobody has studied it, not that a compound is safe.
Is Macimorelin (Macrilen) approved?
And where the numbers on this page come from.Yes. Macimorelin (Macrilen) is FDA approved and available on prescription in the United States.
- Approval statusFDA-approved
- RouteBy mouth (oral)
- CheckedAugust 2026
What has happened recently
FDA-approved in December 2017 as an oral diagnostic for adult growth hormone deficiency. Prohibited in sport at all times by WADA, which names macimorelin explicitly. Drug availability listings indicate the marketed formulations have been discontinued, which is separate from the approval remaining on record.
Banned in drug-tested sport. Most research peptides are prohibited under WADA's S0 category, which covers any substance with no approval from any regulatory authority for human use. That means a compound can be banned without ever being named on the prohibited list. Check with your own anti-doping authority rather than assuming absence from the list means permitted.
You can compare this against the whole library, or read how to check a seller.
- DoseFrom the drug label. The manufacturer tested this range and a regulator reviewed it.
- Vial sizeFrom what vendors typically list; not a recommendation.
- Reviewed24 August 2026
What else is like Macimorelin (Macrilen)?
Others in Growth hormone peptides, side by side.If you're weighing Macimorelin (Macrilen), it's worth reading MK-777, Ipamorelin, and CJC-1295 with DAC in the same class.
An FDA-approved ghrelin agonist, and it is a diagnostic test rather than a treatment.
- Dose
- 0.5 mg per kg, once
- How often
- Single dose for the test
Sold as the next MK-677. No published study, and no source we could confirm.
- Dose
- No established dose
- How often
- No established schedule
A gentle shot that nudges your body to release its own growth hormone.
- Dose
- 0.2 up to 0.3 mg per dose (start low, increase slowly)
- How often
- Daily, often at night
A once-or-twice-weekly shot that keeps your growth hormone raised for days.
- Dose
- 1 up to 2 mg per dose (start low, increase slowly)
- How often
- 1-2x per week
10What these words mean
Show glossary +
What these words mean
- 503A and 503B
- The two kinds of compounding pharmacy in US law. A 503A pharmacy prepares medicine for one named patient. A 503B outsourcing facility makes larger batches under stricter manufacturing rules.
- Agonist
- Something that switches a receptor on. The opposite is an antagonist. It blocks the receptor instead.
- Amino acid
- The building blocks that link together in a chain to make a peptide or a protein. The order they sit in is what makes one peptide different from another.
- Amylin
- A hormone released alongside insulin that slows the stomach emptying and reduces appetite. Several weight loss compounds copy it.
- Analog
- A compound built to copy a natural one with small deliberate changes, usually so it lasts longer or holds onto its target more tightly.
- Animal study
- Research done in rats, mice or other animals. Most findings do not repeat in people, so an animal result is a reason to keep looking. It is not a reason to act.
- Antibody
- A large immune protein, far bigger than a peptide, engineered to lock onto one specific target. These are made by drug companies and are not sold as research powders.
- Bacteriostatic water
- Sterile water with a tiny amount of preservative, used to mix powdered peptides.
- Banned in drug-tested sport
- Prohibited by the World Anti-Doping Agency (WADA); using it can disqualify a competing athlete.
- Bioavailability
- How much of a dose actually reaches your bloodstream. Most peptides survive stomach acid badly, so most of them are injected instead of swallowed.
- Bioregulator
- Very short peptides from a Russian research tradition, usually two to four amino acids long, sold for supporting a specific organ. Human evidence is thin and most of it is published in Russian.
- Blend
- One vial holding more than one compound, mixed together by the seller. Working out a dose means working out each ingredient separately, because they are rarely present in equal amounts.
- Boxed warning
- The most serious warning the FDA puts on a drug label, printed inside a black border. It flags a risk considered severe enough to sit above everything else on the label.
- Bulks list
- The FDA's list of ingredients that compounding pharmacies are allowed to use. A substance can sit under review on it for years without anything being decided either way.
- Certificate of analysis (COA)
- A lab report on a batch of product. It only means something if it names the batch you actually received, comes from an independent lab, and can be checked with that lab.
- Clinical trial
- A study that gives a treatment to people under a written plan and measures what happens. It is the only kind of evidence that can show something works in humans.
- Compounding
- A licensed pharmacy preparing a medicine to order. Being allowed to compound something is not the same as the FDA approving it, and the two get mixed up constantly.
- Concentration
- How strong the mixed peptide is, in milligrams per milliliter (mg/mL). More water makes it weaker; less water makes it stronger.
- Cycle
- A stretch of time using a compound followed by a break. Most cycling patterns come from community practice. Very few have been tested.
- DAC
- Short for Drug Affinity Complex. An attachment added to a peptide so it grabs onto a blood protein and stays in the body for days instead of minutes.
- Dead space
- The small amount of liquid left sitting inside the needle and hub after you inject. On very small doses it can be a real share of what you meant to take.
- Dilute
- Adding more liquid to make a mix weaker. The amount of peptide in the vial does not change. It is just spread through more water, so each draw is bigger.
- Endpoint
- The result a trial said in advance that it would measure. A study can be reported as positive and still have missed the endpoint it set out to hit.
- FDA approved
- Reviewed by the FDA and cleared for a specific use, in a specific form, at a specific dose. Approval for one use is not approval for another, and approval in another country is not approval here.
- Fragment
- A short piece cut out of a larger natural protein. A fragment can behave very differently from the whole protein it came from, so evidence about one does not transfer to the other.
- Ghrelin
- The hunger hormone. Some growth hormone compounds work by copying it, so they can make you noticeably hungrier.
- GHRH
- A natural signal telling the pituitary gland to release growth hormone. Several compounds copy it.
- GHRP
- A second, separate signal that also triggers growth hormone release, through a different door than GHRH. This is why the two types are often used together.
- GLP-1
- A natural gut hormone that lowers appetite and blood sugar. Drugs that copy it, like semaglutide, are used for weight loss.
- Growth hormone secretagogue
- A compound that nudges your body to release more of its own growth hormone, rather than injecting the hormone itself.
- Half-life
- How long a compound stays active in your body. A longer half-life means you inject less often.
- HPLC
- A lab method that separates out everything in a sample so the amounts can be measured. It shows how much of the main ingredient is there. It does not confirm that the main ingredient is the right molecule.
- In vitro
- Done in a dish or a test tube, on cells outside a living body. It is the earliest kind of evidence there is.
- Injection site
- The spot on the body where you inject. Moving it around gives the skin and fat underneath time to recover between doses.
- Intramuscular (IM)
- An injection into a muscle, using a longer needle.
- Intravenous (IV)
- An injection into a vein. It needs training and equipment and is not something to do at home.
- Investigational
- Still being tested in clinical trials and not yet approved or legally sold for general use.
- Lyophilized
- Freeze-dried into a powder so it keeps longer. That is the white cake or dust in the bottom of an unmixed vial.
- Mass spectrometry
- A lab method that weighs molecules to confirm what they are. HPLC answers how much is in the sample. This answers what it is.
- mcg and mg
- Units of dose. 1 milligram (mg) equals 1,000 micrograms (mcg).
- Myostatin
- A natural brake on muscle growth. Several compounds are built to block it, though human results have been far smaller than the animal work suggested.
- Off-label
- A doctor prescribing an approved drug for something other than its approved use. This is legal and common, and it is different from a compound having no approval at all.
- Orphan drug designation
- A status given to treatments for rare conditions to make them worth developing. It is an incentive, not an approval, and a compound can hold it while being approved for nothing.
- PCAC
- The FDA advisory committee that reviews compounding ingredients. It recommends. It does not approve, and the FDA does not have to follow what it says.
- Peer review
- Other scientists checking a paper before a journal publishes it. It filters out some bad work. It does not make a finding true.
- Peptide vs small molecule
- A peptide is a short chain of amino acids. A few items here (like MK-677 or methylene blue) are small molecules, not true peptides, but people use them the same way.
- Placebo
- A dummy treatment given for comparison. Without one it is very hard to tell a real effect apart from expectation and time passing.
- Purity
- The share of a sample that is the intended compound, usually given as a percentage. A high purity number on the wrong molecule is still the wrong molecule.
- Randomized
- Deciding by chance who gets which treatment, so the two groups are comparable. Studies that skip this are much easier to read the wrong way.
- Receptor
- A docking point on a cell that a compound attaches to. If a cell has no matching receptor, the compound does nothing to it.
- Reconstitution
- Mixing a powdered peptide with liquid (bacteriostatic water) so it can be drawn into a syringe.
- Research only
- No approved dose or use in people. Sold for research and not reviewed by the FDA for safety or quality.
- Stack
- Using more than one compound at the same time. Almost no combinations have been tested together in people, so a stack is usually built on guesswork.
- Sterile water
- Water with nothing added to stop bacteria growing. It works for a single dose, but a vial mixed with it should not be kept and used again.
- Subcutaneous
- An injection just under the skin, into the fat layer, usually with a short, thin insulin needle.
- Titrate
- Starting at a low dose and increasing it slowly over time so your body adjusts and side effects stay mild.
- Trial phases
- The stages of human testing. Phase 1 checks safety in a small group, phase 2 looks for an effect, and phase 3 tests it against a comparison in a large group.
- Units (on the syringe)
- The marks on an insulin syringe. 100 units equals 1 mL. They measure how much liquid you draw, not the dose in milligrams.
Guides for this compound
- How to Reconstitute a Peptide
Mix peptide powder with bacteriostatic water, step by step.
- mcg vs mg: The Peptide Dosing Mistake to Avoid
Your vial says mg and your protocol says mcg. Here is the conversion and how to check it.
Last reviewed 24 August 2026
Peptide Decoding is published by Decoded Sciences LLC. We take no payment from vendors for coverage, inclusion or ranking, and our affiliate relationships are disclosed in full.