Hi & Welcome. They may cause harmful interactions if taken all together. 1. Taking Effexor XR together with Dexedrine spansule may increase the effects of Dexedrine, and side effects such as nervousness, anxiety, restlessness, and agitation. This combination can also increase the risk of a rare but serious condition called the serotonin syndrome which is characterized by confusion, hallucination, seizure, extremely high BP, increased heart rate, fever, excessive sweating, shivering, blurred vision, severe muscle spasm, tremor, incoordination, stomach cramp, nausea, vomiting, and diarrhea. In severe cases it may result in coma and even death. 2. Taking Clonazepam while on Effexor XR may increase side effects such as dizziness, excessive drowsiness, confusion, and difficulty concentrating. It may also cause impairment in thinking, judgment, and motor coordination which can result in falls and an increased risk of injuries. So, avoid taking these medications all together. So as per the instructions from your doctor continue taking Clonazepam in the evening till Effexor starts to work, then the Clonazepam can be gradually reduced and discontinued thereafter. Hope these answer your query. Wishing you best of your health. A feed back is appreciated.