How does medicine know where it hurts?

Kavindu (age 24) who came to the clinic that day was very surprised and curious. He looked at the medicine card in his hand, shook his head, and asked me a strange question.

"Doctor, last night I had a terrible toothache. I took a painkiller pill given by the dentist. I swallowed the pill and sent it to my stomach, but within 20 minutes my toothache was gone! So how does this little pill know that it's my tooth that hurts? Does it have some kind of GPS system built into it?" Kavindu asked very honestly.

I smiled and said to Kavindu, "Kavindu, there is no GPS inside the pill. But the way it works inside our body is truly amazing. It's like a messenger going around the city. So today, let's talk about how to find the exact spot where the pill hurts after it goes into the stomach and heal it."

What happens when the medicine enters the stomach? (Absorption)

A pill we take first goes to our stomach and small intestine. There, the acid and fluids in the stomach begin to break the pill down into very small particles.

These dissolved drug particles are absorbed through the walls of the small intestine into our bloodstream. In medical science, this process is called absorption .

Distribution throughout the body through the blood

The drug particles that have entered the blood begin to travel through the blood vessels throughout the body with the heartbeat.

Here, the medicine doesn't just go straight to the sore spot. It travels with the blood to every part of the body, from the head to the toes. It's like watering the entire garden with a hose. Even though the water goes throughout the garden, only the plants that need it absorb it, right? That's how medicine works.

The Lock and Key Model

The best way to understand how a drug works and where it is needed is through the "Lock and Key Model" theory.

Our bodies are made up of billions of cells. Each of these cells has small "locks" on its surface made of specialized proteins. In medicine, we call these receptors .

The chemical particles in the pills we take are like specially designed "keys." As these keys travel through the bloodstream throughout the body, they attach to the cell that has the exact lock (receptor) they fit into.

• How painkillers work: When a tooth hurts, the cells in the tooth produce chemicals that signal pain. The painkiller travels through the bloodstream and blocks the receptors on the nerve cells that carry those pain signals to the brain. Then, the pain message doesn't go to the brain, so we don't feel the toothache.
• How allergy medicine works:By blocking the receptors that bind to the chemical histamine that causes allergies, symptoms such as sneezing and itching are eliminated.

Dealing with Enzymes

In addition to receptors, there are a group of workers in our body that speed up each chemical process. They are called enzymes .

Some medications work by temporarily stopping the activity of these enzymes. For example, medications like Panadol (Paracetamol) work by stopping the activity of enzymes in the body that are activated when we have aches and fevers.

Why do we get side effects?

Because drugs travel throughout the body, they can sometimes bind to receptors in places other than where we want them.

For example, some medications for stomach ulcers can travel through the bloodstream and bind to receptors in the brain, making us feel sleepy. This is called a side effect .

Modern Targeted Therapies and Nanotechnology

Although old medicines affected the entire body, modern medicine has advanced so much that modern medicines are now like missiles that hit their target.

• Nanotechnology: This allows drugs to be encapsulated in nanoparticles, millions of times smaller than a hair, and then delivered directly to diseased cells (e.g., cancer cells).
• Antibody Therapies: Drugs have been developed that recognize and attack specific markers on the surface of cancer cells, greatly reducing damage to healthy cells and side effects.

Medicine from nature

Many of the Western medicines we see today originated from natural plants and fungi.

• Aspirin: Aspirin, the world's most famous painkiller and blood thinner, was first discovered from the bark of the willow tree.
• Penicillin: The first antibiotic was discovered from a mold called Penicillium notatum.

🚨 Precautions and medical advice

Although medicines are very beneficial to the body, their misuse can be life-threatening.

When to see a doctor immediately:

• If you develop symptoms of severe allergy (Drug Allergy/Anaphylaxis) such as difficulty breathing, swelling of the lips and face, or red spots on the skin within a few hours of taking a certain medicine.
• If you accidentally take more than the dose prescribed by your doctor (overdose).
• If symptoms of gastric ulcers or kidney problems develop due to continued use of painkillers without any medical advice.

Do's & Don'ts

Scientific sources (References)

• 📚 Medicines A to Z - NHS
• 📚 An overview of pharmacodynamic modeling, ligand-binding approach and its application in clinical practice - PMC