What phenomenon describes John needing to drink two six-packs of beer to achieve the same effect he felt from one six-pack?

The phenomenon that John is experiencing is known as tolerance. Tolerance occurs when an individual requires an increased amount of a substance to achieve the same effects that were previously attained with a lower dose. In John's case, he initially felt a certain level of intoxication or effect from one six-pack of beer; however, due to repeated use, his body has adapted to the presence of alcohol, necessitating a higher quantity (two six-packs) to produce the same effect.

This concept is an important aspect of substance use and addiction, as it can lead to escalating consumption and potential health risks. Tolerance is a significant marker in the development of substance use disorders and plays a crucial role in understanding an individual’s relationship with alcohol.

Understanding this can help clarify other concepts, such as dependence, which relates to the body's adaptation resulting in withdrawal symptoms when the substance is reduced or stopped, but is distinct from the gradual need for increased amounts to achieve the same effect.