Lipidation, albumin-hitchhiking, PEGylation and DAC — the real magic behind weekly drugs
The core problem
Natural peptides are usually cleared from the body in minutes. Native GLP-1's half-life is roughly 2 minutes — the enzyme DPP-4 chops it up almost immediately.1 A drug you'd have to inject every few minutes is useless. The entire modern peptide-drug industry is, in a sense, the science of making short-lived peptides last.
The toolkit
A fatty-acid chain lets a peptide hitch onto albumin, hiding it from clearance — the trick that turns a 2-minute molecule into a once-weekly drug.
Lipidation (acylation): attach a fatty-acid chain so the molecule reversibly binds albumin — the blood's most abundant protein — hiding from clearance. Semaglutide's C18 diacid chain pushes its half-life to ~165 hours (weekly).1
Amino-acid substitutions that make the peptide resist DPP-4.
PEGylation: attach polyethylene-glycol to increase size and slow clearance.
DAC (Drug-Affinity Complex): a group that binds albumin — the reason CJC-1295 with vs without DAC behaves so differently (days vs minutes).
Why 'No-DAC' vs 'DAC' matters
Read the suffix: the same core peptide with an albumin-binding group can go from short-acting to multi-day. "No-DAC" isn't a weaker version — it's a different kinetics profile. Recognizing modifications (DAC, acylation, PEG) tells you how often something is meant to act and how long it lingers.
The lesson
When you see a peptide marketed as "long-acting" or "weekly," ask what modification makes it so. The mechanism (the receptor) tells you what it does; the half-life engineering tells you how long and how often.
Further reading — primary sources
Peptide half-life extension — lipidation, albumin binding, PEGylation (review). ACS Med. Chem. Lett.
For educational and research purposes only. This content is not medical advice. Compounds referenced are research use only unless noted as approved drugs, and nothing here is an instruction to use, prepare, or administer anything. Free Peptide University does not sell compounds.