Have you ever taken a pill and wondered how the drug knew where to go after you swallowed it? Or, how does a heart medication know to go to the heart? Well, the answer is, it doesn’t!
The “lock and key model” shows us how drugs work. In this model, the drug is the key and the receptors for the drug are the locks. Drugs are designed to attach themselves to receptors within the body based on their shape.
Once swallowed, the medication is absorbed into your bloodstream and distributed throughout your body. When it comes into contact with a receptor it recognizes, it binds to the receptor and does one of the following:
- Activates the receptor inducing a response
- Blocks the receptor and prevents a response
There are an unknown number of different receptors in your body. Medications are designed with the goal of only fitting one receptor and thus only activating one type of response. Just like a key is only made to open one specific lock.
If it was possible to create a drug that truly only interacted with one type of receptor in the body, there would be no such thing as side effects.
The problem with the lock and key model is that it is the ideal and not the reality. Unfortunately, while a drug interacts with one receptor more than others, it is also able to interact with unintended receptors that have a similar structure. When a drug binds to a receptor that it isn’t supposed to, the result is an unwanted response or side-effect.