Dextromethorphan (AVP-923), a σ1 receptor agonist, has been found to have multiple mechanisms of action that could be beneficial in AD, such as anti-inflammatory and antioxidant effects, modulation of neurotransmitters, and a neuroprotective effect by inhibiting Aβ aggregation and tau hyperphosphorylation in AD [186,187,188]. This evidence concerns the gene MAPT and Alzheimer disease.