Yes, indeed - Chemistry! In order to understand the problem, a look into the molecular similarities might be of great use. Last weekend, Kayla -- who writes on this blog and other sites -- finished up a blog post on "opioids". You can access that blog post by clicking -- HERE. Kayla takes the reader on a short journey starting at the outset with the stated fact that over 150,000 plant and microorganism derived "bioactive" compounds are found in nature. As she points out some of which are active in humans. One class of "bioactive" compounds are the opioid family (shown below):
Source: Ranndy Glasbergen
Structural similarities were shown to reveal that the active ingredient in cough syrup (Dextromethorphan -- derived from codeine) is not very different from the molecular structure of "vicodon" -- which is commonly abused by the public. Although, Dextromethorphan has a lower risk of abuse. The manner in which the drugs target a given "active site" forms a range. This is due to the molecular structure. Each molecular structure (in a family) has an "affinity" for a given "active site" in the body. Drugs with a higher affinity to hit a given "active site" result in being labeled as "more potent." Potency can be related to abuse. Other drugs might hit a range of "active sites" which might contribute to the phenomenon of "side effects" associated with a given drug. These drugs might not be preferable to an addict due to unwanted side effects.
The blog post is a great primer on the molecular similarities and differences -- worth reading. Especially for the readers who are interested in the content that is presented on this site and "Mike Thinks". With that in mind, I hope that you enjoy the short primer on opioids written by Kayla. Have a great day!