Substance Sim: Advanced Pharmacokinetic Simulation Engine 🧪

Substance Sim is a scientific research platform designed to model the pharmacokinetics (PK) and pharmacodynamics (PD) of psychoactive and medical substances. Unlike simple calculators, it uses differential equations to simulate absorption, distribution, metabolism, and excretion (ADME) processes.

🚀 Key Features

• Advanced Math Engine: Implements the Bateman Function for dual-phase (absorption & elimination) kinetics.
• Pharmacodynamics: Uses the Hill Equation to model the non-linear relationship between concentration and biological effect.
• Neuroadaptation Model: Simulates tolerance build-up over time based on cumulative exposure (AUC).
• Multi-Dose Simulation: Supports complex dosing schedules (e.g., "3 doses every 4 hours") to analyze accumulation and toxicity.
• Medical & Psychoactive Models: Includes models for Caffeine, Alcohol, Nicotine, and Paracetamol (Liver Toxicity).

🛠️ Tech Stack

• Backend: Node.js, Express.js (REST API)
• Database: MongoDB (Scientific Data Storage)
• Frontend: HTML5, Bootstrap 5, Chart.js (Dual-Axis Visualization)
• Math: Custom implementation of PK/PD differential equations

📦 Installation & Setup

1. Clone the repository:

   git clone https://github.com/YusufOztoprak/substance-sim.git
   cd substance-sim

2. Install dependencies:

   npm install

3. Configure Environment: Create a .env file (or use the provided .env.example):

   PORT=3000
   MONGO_URI=mongodb://localhost:27017/substance_sim

4. Seed the Database (Crucial Step): Populate the database with scientific data (Caffeine, Alcohol, Nicotine, Paracetamol):

   npm run seed

5. Start the Simulation Engine:

   npm start

6. Launch: Open http://localhost:3000 in your browser.

🔬 The Science Behind It

This engine goes beyond simple half-life calculations. It implements:

1. The Bateman Function (Concentration)

$$ C(t) = \frac{D \cdot k_a}{V_d (k_a - k_e)} \left( e^{-k_e t} - e^{-k_a t} \right) $$

Simulates the rise (absorption) and fall (elimination) of substance levels.

2. The Hill Equation (Effect)

$$ E = \frac{E_{max} \cdot C^n}{EC_{50}^n + C^n} $$

Models the sigmoidal dose-response curve.

3. Tolerance (Neuroadaptation)

$$ Tolerance(t) = 1 - e^{-\alpha \cdot \int C(t) dt} $$

Calculates how the body adapts to the substance over time.

📡 API Endpoints

Method	Endpoint	Description
GET	/api/substances	Returns list of substances with PK parameters.
POST	/api/simulate	Runs the simulation engine. Body: { substanceId, dose, weight, doses, interval }

📄 License

This project is licensed under the MIT License. See the LICENSE file for details.