Pharmacokinetics

Pharmacokinetics (PK) describes what the body does to the drug. PK is universally summarized by the ADME framework: Absorption (rate and extent into circulation), Distribution (transport throughout tissues and binding to plasma proteins), Metabolism (enzymatic breakdown by peptidases and hepatic enzymes), and Excretion (renal elimination or biliary clearance).

Peptides typically have challenging pharmacokinetic profiles because they may undergo rapid renal filtration and degradation within minutes. Modern therapeutic peptides overcome this via chemical acylation (fatty acid chains binding serum albumin) to dramatically extend circulation.

Pharmacokinetics explains how one peptide family can produce medicines that last minutes or a week. Native GLP-1 is cleared within about two minutes, while semaglutide, which carries a fatty-acid chain that binds reversibly to albumin and amino-acid substitutions that resist breakdown, has a half-life of about a week in humans. Those design changes, described by the drug’s developers, are what make it a long-acting medicine.

Many claims about unapproved peptides skip pharmacokinetics entirely. A 2025 systematic review of BPC-157 reported that it is metabolised in the liver, has a half-life of less than 30 minutes and is cleared by the kidneys, but the evidence base was almost entirely preclinical. Without human pharmacokinetic studies, nobody can say how much of a product reaches the bloodstream or target tissues, how long it stays, or how much this varies between people.

Route of administration is a pharmacokinetic question too. Unmodified peptides usually have very limited oral bioavailability, because enzymes break them down and they cross the intestinal wall poorly. Products sold as capsules, nasal sprays or creams therefore need their own evidence that the peptide is absorbed intact, rather than borrowing results from injected forms used in animal studies.

“Half-life tells you exactly how long a drug works”

Half-life is the time it takes for the blood concentration to fall by half. It influences how long a drug acts, but effects can outlast or fade before measurable blood levels, depending on the receptor, downstream signalling and tissue binding. It also takes several half-lives for a drug to clear almost completely, which is why side effects of long-acting drugs can persist after stopping.

“Any peptide can be taken by mouth”

Most cannot. Peptides are broken down by digestive proteases and cross the gut wall poorly, so oral bioavailability is usually very low. Oral semaglutide works only because it is formulated with an absorption enhancer designed for that purpose. Claims that an ordinary peptide works as a capsule or drink need direct human absorption data, not assumptions.

“Animal pharmacokinetics predict human pharmacokinetics”

Clearance, half-life and protein binding often differ between species. During semaglutide’s development, for example, its plasma half-life after intravenous administration in mini-pigs was about 46 hours, much shorter than the roughly one-week half-life later seen in humans. Scaling from animal data gives a starting estimate, not an answer, which is why human pharmacokinetic studies are required.

What is the half-life of semaglutide?

Semaglutide has an elimination half-life of about one week (around 168 hours) in humans. This long duration comes from a fatty-acid side chain that binds reversibly to albumin in the blood and from amino-acid changes that protect it from breakdown by the enzyme DPP-4. By comparison, the body’s own GLP-1 lasts only about two minutes in the circulation.

What does ADME stand for?

ADME stands for Absorption, Distribution, Metabolism and Excretion, the four processes that together describe a drug’s pharmacokinetics. Absorption is how the drug enters the bloodstream, distribution is where it travels, metabolism is how it is broken down, and excretion is how it leaves the body, mainly through the kidneys or bile.

Why do most peptides have short half-lives?

Protease and peptidase enzymes that cut peptide bonds are found throughout the body, not just in the liver, so unmodified peptides are broken down quickly. Small peptides are also freely filtered by the kidneys. Drug developers extend half-life by substituting amino acids, modifying the ends of the chain, or attaching the peptide to albumin-binding groups, polymers or larger proteins.

What is the half-life of BPC-157?

Reliable human data do not exist. A 2025 systematic review reported a half-life of less than 30 minutes, with metabolism in the liver and clearance by the kidneys, but these findings come from preclinical research rather than controlled human pharmacokinetic studies. BPC-157 is not FDA-approved, and how it behaves in people has not been properly characterised.