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Venlafaxine is a serotonin and noradrenaline reuptake inhibitor (SNRI) agent. Besides serotonin and noradrenaline reuptake inhibition effect it has also little effect on dopamine reuptake inhibition. The power of reuptake inhibition is dose dependent. The serotonin and noradrenaline reuptake inhibitors like venlafaxine have very rare side- effects on reproductive and endocrine systems. The literature reveals only one case about venlafaxine causing galactore and 2 cases of dose related rise in prolactin levels. In this paper, we report a 70 years old female patient with vascular dementia. She had received 20 mg/day escitalopram treatment because of depressive mood but had no benefit. We changed the medical treatment to 75 mg/day venlafaxine and not having proper answer, we raised the dose to 150 mg/day. As soon as the dose was titrated up, the patient started to have symptoms like nausea, vomiting, weight loss and sleepiness that were progressive day by day. Upon investigation of the possible cause of the symptoms, hyperprolactinemia was identified and the mechanisms leading to hyperprolactinemia were further investigated. Magnetic Resonance (MR) imaging for adenomas were free of proof. Then the drugs used by the patient were evaluated. Venlafaxine was the only possible suspect as the symptoms started after its administration and the dose of the drug was reduced to 75 mg/day and the laboratory showed a decrease in prolactin levels to normal. Data presented in this report is consistent with the previous case reportings about dose related elevations of prolactin levels. With this case report, we wanted to attract the attention to a very rare adverse effect of venlafaxine that is believed to be dose related and try to find answers about the possible mechanisms.