Reta half-life is about six days, which is why retatrutide is dosed once weekly. Learn how long reta stays in your system and whether it shows up on drug tests.
Retatrutide, commonly nicknamed "reta," has a half-life of about six days, which is why it is designed for once-weekly subcutaneous injection. That long half-life also means the drug lingers: after a final dose, it takes roughly 30 days — about five half-lives — for nearly all of it to leave your system. Retatrutide is not FDA-approved for human use in the United States.
What Is Reta (Retatrutide)?
Retatrutide (LY3437943) is an investigational triple agonist developed by Eli Lilly. It activates three hormone receptors at once: GIP, GLP-1, and glucagon.
In a Phase 2 trial published in the New England Journal of Medicine, adults with obesity who received 12 mg weekly lost an average of about 24% of their body weight over 48 weeks. Those results explain the high search interest in the drug even though it remains unapproved.
Reta Half-Life: The Core Number
A half-life is the time required for the body to eliminate half of a drug dose. Reta half-life estimates cluster around six days, with reported values generally falling between five and seven days.
Drugmakers engineer incretin peptides this way on purpose. Modifications that resist the DPP-4 enzyme and bind the peptide to albumin slow clearance, which is what makes weekly dosing possible instead of daily injections.
| Compound | Approximate half-life | Typical dosing |
|---|---|---|
| Retatrutide (reta) | ~6 days | Once weekly |
| Semaglutide | ~7 days | Once weekly |
| Tirzepatide | ~5 days | Once weekly |
| Dulaglutide | ~5 days | Once weekly |
| Liraglutide | ~13 hours | Once daily |
Short-acting research peptides clear far faster by comparison. The semax half-life is measured in minutes, which is why that compound has to be dosed repeatedly through the day.
How Long Does Reta Stay in Your System?
Pharmacokinetics uses a simple rule of thumb: about five half-lives must pass before a drug is considered effectively cleared. At a six-day half-life, that works out to roughly 30 days.
Steady state is the mirror image of that math. With weekly dosing, retatrutide accumulates until blood levels plateau after about four to five weeks, which is also why dose increases in trials are spaced roughly four weeks apart.
| Time after last dose | Approximate amount remaining |
|---|---|
| Day 6 (1 half-life) | ~50% |
| Day 12 (2 half-lives) | ~25% |
| Day 18 (3 half-lives) | ~12.5% |
| Day 24 (4 half-lives) | ~6% |
| Day 30 (5 half-lives) | ~3% or less |
So when people ask how long does reta stay in your system, the practical answer is two to four weeks for most of the drug to clear and about a month for the remainder. The same math answers how long does reta take to leave your system: there is no single day when it is suddenly gone, and individual clearance varies with body weight, kidney function, and dosing history.
How Long Does Reta Take to Kick In After Injection?
Half-life describes elimination, not onset, so the two timelines can look very different. Most trial participants reported appetite changes within the first one to two weeks of starting treatment.
- Days 1–3: Drug levels rise toward peak, and some people notice reduced appetite or mild nausea early.
- Weeks 1–2: Appetite suppression and gastrointestinal side effects are usually most noticeable.
- Weeks 4–8: Measurable weight change typically begins to show up on the scale.
- Months 3–12: Most of the weight loss reported in trials accumulates over months, not weeks.
Because the drug builds up with each weekly injection, effects often feel stronger in week four than in week one at the same dose. Retatrutide is not a cure for obesity, and outcomes depend on diet, activity, and individual physiology.
Does Reta Show Up on a Drug Test?
Standard workplace drug panels do not test for retatrutide. A typical five-panel urine screen looks for amphetamines, opioids, cocaine, THC, and PCP, none of which are related to incretin peptides.
Specialized testing is a different story. Anti-doping laboratories and some research programs use liquid chromatography–mass spectrometry assays that can be built to detect specific peptides, including investigational ones.
Detection windows also vary across drug classes. The somatropin half-life is only a few hours, so growth hormone misuse is usually flagged through indirect biomarkers rather than the hormone itself. Retatrutide's six-day half-life would give testers a much wider window, but only if the test is designed to look for it.
What Affects Reta Half-Life and Clearance?
- Body weight and composition: larger body mass can alter how a drug distributes and clears.
- Kidney function: reduced renal clearance can prolong exposure to many peptides.
- Liver health: the liver handles the breakdown of many drugs and peptides.
- Dose and frequency: weekly dosing causes accumulation, so total exposure rises over the first month.
- Injection technique: absorption from subcutaneous tissue varies with site and local blood flow.
Retatrutide is still being studied, so published human data on how these factors shift its half-life remain limited.
People who follow peptide research often compare molecules across categories. Questions about the aod 9604 half-life and the cagrilintide half-life come up in the same conversations because both are studied for fat loss, even though their pharmacology differs from retatrutide's. Other compounds are not comparable at all — the melanotan ii half life, for example, describes a completely different drug with a much shorter duration of action.
Safety and Legal Status
Retatrutide is not FDA-approved, is not available by prescription, and is not dispensed by licensed pharmacies. Powder sold online as "research grade" retatrutide is not verified for identity, purity, or sterility, and dosing errors with unregulated peptides have caused serious harm.
In trials, the most common side effects were gastrointestinal: nausea, diarrhea, vomiting, and constipation. Anyone considering a GLP-1–class medication should talk with a healthcare professional about approved options and personal risks.
Frequently Asked Questions
How long does reta stay in your system after the last dose?
Most of the drug clears within two to four weeks of a final injection, and it takes roughly 30 days — about five half-lives — for retatrutide to be effectively eliminated. Retatrutide has a half-life of approximately six days, so side effects such as nausea and appetite suppression can fade gradually rather than all at once.
Does reta show up on a standard drug test?
No. Routine five-panel or ten-panel workplace urine screens look for substances like amphetamines, opioids, cocaine, THC, and PCP, and they do not include peptide drugs such as retatrutide. Specialized mass-spectrometry assays used in anti-doping or research settings can be designed to detect it if testers are specifically looking.
How long does retatrutide take to start working?
Many trial participants noticed appetite changes within one to two weeks of the first injection, and noticeable weight change usually appears over four to eight weeks. Because retatrutide accumulates with weekly dosing, its effects often feel stronger at week four than at week one, and most weight loss in trials built up over several months.
This page provides educational research information and does not replace medical advice, diagnosis, or treatment.