The most common adverse side effects associated with Effexor usage are nausea, dry mouth, dizziness, nervousness, anxiety, sexual dysfunction
etc. Abrupt discontinuation of Effexor can lead to more severe side effects - insomnia, dizziness etc. Effexor should be tapered over a week under the close supervision by a psychiatrist to avoid any withdrawal symptoms. I would recommend that he should contact his psychiatrist as soon as possible for appropriate treatment.