While pharmaceutical drugs are often developed to target particular bodily systems and provide particular effects, Mother Nature is not always so exacting. The effects of organic compounds can be many and can vary from person to person. Oftentimes herbal compounds can have both desired effects and unwanted effects. We call these unwanted effects adverse side effects.
In order to determine if an effect is an adverse side effect, you need to know what the desired effects are. The effects which are desired by one user may not be desired by another user.
Let’s look at an example of how CBD might work differently for different people. Some people use CBD oil in order to support a good night of rest but may also feel drowsiness during the day. If you want to feel awake during the day, as most do, feeling sleepy would be an unwanted side effect.