Large Language Models (LLMs) have revolutionized numerous applications, making them an integral part of our digital ecosystem. However, their reliability becomes critical, especially when these models are exposed to misinformation. This paper primarily analyzes the susceptibility of state-of-the-art LLMs to factual inaccuracies when they encounter false information in a Q&A scenario, an issue that can lead to a phenomenon we refer to as knowledge drift, which significantly undermines the trustworthiness of these models. We evaluate the factuality and the uncertainty of the models’ responses relying on Entropy, Perplexity, and Token Probability metrics. Our experiments reveal that an LLM’s uncertainty can increase up to \( 56.6\%\) when the question is answered incorrectly due to the exposure to false information. At the same time, repeated exposure to the same false information can decrease the models’ uncertainty again ( \(-52.8\%\) w.r.t. the answers on the untainted prompts), potentially manipulating the underlying model’s beliefs and introducing a drift from its original knowledge. These findings provide insights into LLMs’ robustness and vulnerability to adversarial inputs, paving the way for developing more reliable LLM applications across various domains. The code is available at https://github.com/afastowski/knowledge_drift .