PolyDiscipline
Courses

CoursePsychopharmacology Introduction

The drug-action atlas

Enter through a molecule, a synapse, or a brain circuit. Change the conditions and trace what happens next.

Explore the system

The first-pass detour

Compare the gastrointestinal → portal → liver route with direct or mucosal entry into systemic circulation.

The first-pass detour
Oral → Systemic circulation → Brain / site of action → Liver → KidneysBrain / site of actionLungsSystemic circulationLiverGastrointestinal tractKidneysPortal circulationOralGastrointestinal tract
Oral · Gastrointestinal tract

Intestinal and hepatic first pass can reduce availability

All routes can reach the liver later through systemic circulation.

Often slower and variable

Convenient; absorption depends on formulation, food, and gastrointestinal factors

Aspirin example in Chapter 1

Mechanism and exceptions

Course example: swallowed dimethyltryptamine (DMT) is rapidly metabolized by monoamine oxidase. This illustrates first-pass loss; it is not an instruction for modifying or combining drugs.

On a small screen, pan the diagram or increase zoom. Named controls provide the same exploration by keyboard.

Predict, then check

Does avoiding first-pass entry mean a drug never reaches the liver?

Exploration and predictions are practice. They do not award mastery or XP.

Sources and model limits

Original schematic. Positions show relationships; structures and concentrations are not to scale.

  • Julien's Primer of Drug Action · 15 · 1 · The first-pass detour · PDF 10, 13 · 1.3
  • Professor deck 4 · DMT / first-pass metabolism · PDF 42, 43