About The most common minor side effects during clinical trials include short-term nausea (which can be reduced by taking the medication with food), sleepiness, dry mouth, dizziness, constipation, nervousness, sweating, weakness, ejaculation/orgasm problems, and loss of appetite. A small percentage (about five percent) of patients, usually those taking higher doses, will develop elevated blood pressure. Therefore, patients taking Effexor should have their blood pressure checked regularly. Some agitation has been noticed at higher dosages.