A study investigated the long-term effects of metformin treatment on cognition in Alzheimer’s disease (AD) model mice. Metformin, a common anti-diabetic drug, was administered to transgenic 3xTg-AD and non-transgenic (NT) C57BL/6 mice for 1 and 2 years, respectively. Behavioral assessments were conducted using touchscreen operant chambers to evaluate motivation, attention, memory, visual discrimination, and cognitive flexibility. In younger NT mice, metformin improved attention, inhibitory control, and associative learning. However, in older mice, chronic metformin treatment led to impairments in memory retention and discrimination learning. In AD mice, metformin caused learning and memory impairments, increased levels of β-amyloid oligomers, plaques, phosphorylated tau, and GSK3β expression. No significant changes were observed in potential confounding factors such as motivation, locomotion, appetite, body weight, blood glucose, and serum vitamin B12. Metformin also enhanced the amyloidogenic pathway in db/db mice and reduced synaptic markers in primary neurons. These findings suggest that the repurposing of metformin for AD should be carefully reconsidered. The study highlights the importance of long-term behavioral outcomes in drug repurposing for AD, as short-term biological effects may not reflect the consequences of lifelong use. The results indicate that chronic metformin treatment impairs multi-domain cognition in aged mice and exacerbates AD pathology, including increased levels of Aβ and p-tau, and elevated expression of GSK3β and AMPKα1 in the hippocampus. The study underscores the need for further research to understand the mechanisms behind metformin’s effects on cognition and AD pathology.A study investigated the long-term effects of metformin treatment on cognition in Alzheimer’s disease (AD) model mice. Metformin, a common anti-diabetic drug, was administered to transgenic 3xTg-AD and non-transgenic (NT) C57BL/6 mice for 1 and 2 years, respectively. Behavioral assessments were conducted using touchscreen operant chambers to evaluate motivation, attention, memory, visual discrimination, and cognitive flexibility. In younger NT mice, metformin improved attention, inhibitory control, and associative learning. However, in older mice, chronic metformin treatment led to impairments in memory retention and discrimination learning. In AD mice, metformin caused learning and memory impairments, increased levels of β-amyloid oligomers, plaques, phosphorylated tau, and GSK3β expression. No significant changes were observed in potential confounding factors such as motivation, locomotion, appetite, body weight, blood glucose, and serum vitamin B12. Metformin also enhanced the amyloidogenic pathway in db/db mice and reduced synaptic markers in primary neurons. These findings suggest that the repurposing of metformin for AD should be carefully reconsidered. The study highlights the importance of long-term behavioral outcomes in drug repurposing for AD, as short-term biological effects may not reflect the consequences of lifelong use. The results indicate that chronic metformin treatment impairs multi-domain cognition in aged mice and exacerbates AD pathology, including increased levels of Aβ and p-tau, and elevated expression of GSK3β and AMPKα1 in the hippocampus. The study underscores the need for further research to understand the mechanisms behind metformin’s effects on cognition and AD pathology.