Peptide Half-Life Reference: Dosing Frequency & Duration

Half-life is the time it takes for the plasma concentration of a compound to fall by half. It directly determines three things: how often the compound must be dosed, how quickly it reaches steady state, and how long it persists after discontinuation.

A peptide with a half-life of 2 minutes (native GLP-1) must either be infused continuously or chemically modified to be clinically useful. A peptide with a half-life of 7 days (semaglutide) can be dosed once weekly. A peptide with a half-life of 8 days (CJC-1295 with DAC) can be dosed as infrequently as every 7-10 days.

Steady state — the concentration at which drug input and clearance balance — is typically reached after about 4-5 half-lives of consistent dosing. For semaglutide this means about 4-5 weeks. For CJC-1295 with DAC, about 30-40 days. For short half-life peptides like ipamorelin (~2 hours), steady state is reached within a day if multi-dosed but steady state is not the clinical goal — pulsatile exposure is.

Half-life also predicts washout. After discontinuation, it takes roughly 5 half-lives for >95% clearance. Semaglutide at 7 days means ~5 weeks of residual activity after the last dose. This matters for conception planning, surgery, and drug interactions.

Representative half-life values from published pharmacokinetic data. Values vary by formulation, dose, and individual physiology; these are typical clinical ranges.

GLP-1 and incretin class: - Native GLP-1: ~2 minutes (infusion only) - Exenatide (immediate release): ~2.4 hours (twice daily) - Liraglutide: ~13 hours (once daily) - Semaglutide: ~7 days (once weekly) - Tirzepatide: ~5 days (once weekly) - Retatrutide: ~6 days (once weekly, investigational)

Growth hormone axis: - Sermorelin: ~10-20 minutes (daily at bedtime) - GHRP-2 / GHRP-6: ~15-20 minutes (2-3x daily) - Ipamorelin: ~2 hours (1-3x daily) - CJC-1295 without DAC (Mod GRF 1-29): ~30 minutes (2-3x daily) - CJC-1295 with DAC: ~6-8 days (1-2x weekly) - Tesamorelin: ~26-38 minutes (daily) - MK-677 (ibutamoren, oral): ~24 hours (once daily)

Healing and recovery: - BPC-157 (subcutaneous): ~4-6 hours (typically daily dosing) - TB-500 / Thymosin Beta-4: ~2-3 hours (1-2x weekly at high dose) - GHK-Cu (topical): not applicable systemically; skin retention hours to days

Other: - PT-141 (bremelanotide): ~2.7 hours (as-needed dosing) - Thymosin Alpha-1: ~2 hours (2-7x weekly depending on indication) - Epithalon: ~30 minutes (cycled daily courses) - MOTS-c: ~30 minutes to 2 hours (investigational)

Long half-life advantages. Weekly dosing improves adherence, smooths peak-to-trough concentration variation, and avoids the sharp rises and falls associated with short-acting compounds. This is why semaglutide and tirzepatide have largely replaced exenatide and liraglutide in weight-loss practice — same mechanism, far less burdensome schedule.

Long half-life disadvantages. Slow wash-out means side effects persist long after discontinuation. Dose titration is slower (each step takes 4-5 weeks to stabilize). Drug interactions have a wide window. Pregnancy planning requires a 2-month pre-conception washout for semaglutide.

Short half-life advantages. Allows pulsatile exposure that mimics natural hormone patterns — this is the rationale for ipamorelin and Mod GRF 1-29 combinations, which pulse GH release in a pattern more similar to endogenous rhythms than once-weekly long-acting compounds would produce. Dose adjustment is fast; side effects clear quickly.

Short half-life disadvantages. Multiple injections per day (ipamorelin), strict timing requirements (sermorelin at bedtime), and higher cumulative injection burden.

Choosing. FDA-approved indications have long-acting products because adherence is the dominant driver of real-world effectiveness. Research protocols studying pulsatile hormone physiology lean toward short-acting molecules. Both have legitimate uses.

Native peptides are degraded rapidly by proteases in blood and tissue. Modern medicinal chemistry extends half-life through several strategies:

Fatty acid acylation (lipidation). Attaching a long fatty acid chain allows the peptide to bind reversibly to serum albumin, sheltering it from proteases and reducing renal filtration. Semaglutide (C18 fatty di-acid) and liraglutide (C16 fatty acid) use this approach. Albumin acts as a circulating depot.

DPP-4 resistance. Modifying the amino acids at the DPP-4 cleavage site (position 2 of GLP-1) blocks the primary degradation enzyme. Exenatide substitutes glycine at position 2; semaglutide uses aminoisobutyric acid (AIB). This alone extends half-life from minutes to hours.

PEGylation. Attaching polyethylene glycol chains increases molecular size beyond the renal filtration threshold (~50 kDa) and shields the peptide from proteases. Pegvisomant uses this approach.

DAC (Drug Affinity Complex). CJC-1295 with DAC includes a maleimide group that covalently bonds to albumin cysteine 34 in vivo, producing an extremely long half-life (~8 days) compared to the unmodified Mod GRF 1-29 (~30 minutes).

Depot formulations. Tesamorelin is a native GHRH analog with no half-life extension; convenience comes from once-daily dosing rather than molecular engineering. Some peptides use microsphere or in situ forming depot formulations for sustained release over weeks.