Some terminology will help you here. Therapeutic effects are the effects we are trying to stimulate to help the client. 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.