Side effects are any effects other than the therapeutic effect. Adverse effects are undesirable effects. Toxic effects result in poisoning or damage. Teratogenic effects cause abnormal fetal development. Carcinogenic or oncogenic effects cause cancer.
Iatrogenic effects are damage or illness conditions caused by the treatment.
Idiosyncratic effects are quirky, unexpected, unusual effects. Paradoxic effects are medication effects which are opposite to the usual effect. As you will remember, placebo effects are caused merely by belief that the treatment will help. The use of terminology can get a little tricky, however, because some medications can be used for several reasons, so the therapeutic effect when using it for one disorder may be a side effect when using it for another disorder. And the power of hope you instill as you give chemically active medications with a positive attitude may promote a placebo effect as well.