Therapeutic effects are the good things that can happen to you from taking the drug and the reason the drug is recommended, used or prescribed. For example, the therapeutic effect of ampicillin is to destroy the bacteria that cause infections. Side effects or cautions are common symptoms or signs that occur when you use a certain drug. Even though these side effects are minor, they can be irritating. For example, ampicillin can cause diarrhea, a nonallergic rash, or a tendency to get a yeast infection.
Theophylline can cause shakiness, nausea, hyperactivity or a rapid heartbeat.
Adverse reactions are so serious reactions that occur in some people who use a drug. The effects are no serious that the person has to stop taking the drug and probably never use it again. For example, ampicillin can cause an allergic reaction in some children ranging from hives to an anaphylactic reaction-signs of a true allergy to a medicine. Idiosyncratic reactions are unusual reactions to a medicine that aren't real allergy but are unique to the individual. In fact, the reaction may be the exact opposite of the reaction you expect.