The aim of this review is to describe side effects of five antidementives which are approved by the United States Food and Drug Administration (FDA); four acetylcholinesterase inhibitors and one glutamate - or N-metyl-D-aspartat receptor antagonist - memantine. The antidementives are well tolerated and undesired effects are rare; except hepatotoxicity of tacrine and gastrointestinal side effects of donepezil, rivastigmine, galantamin and tacrine that result from acetylcholinesterase inhibition. Nausea, diarrhea, vomiting, and weight loss are the most common side effects of the acetylcholinesterase inhibitors. Significant cholinergic side effects can occur in patients receiving higher doses; often they are related to the rate of initial titration of medication. Memantine is the first noncholinesterase inhibitor indicated for Alzheimer's disease. The side effects which may occur during the treatment with memantine are constipation, dizziness, headache and confusion. These effects if appears are mild end transient.