Side effect: A side effect is an effect of a drug, chemical, or other medicine that is in addition to its intended effect.
Therapeutic effect/ Adverse effect: An adverse effect is a harmful, undesirable effect that that result from a medication or other intervention.

Effects:

1- Side Effects can be both therapeutic and harmful.
2-Adverse Effects are generally harmful and undesirable.

Prior knowledge:

1-Side Effects are usually expected by the doctor.
2-Adverse Effects are not expected by the doctor.

Effect on the treatment: 

1-Side Effects generally do not hinder the main effect of the drug.

2-Adverse Effects can hinder the treatment and lead to more complications.

Severity: 

1-Side Effects are mild and self-resolving when compared to adverse effects.

2-Adverse Effects are more severe and life threatening.