Even those who advocate most strongly for the legalization of marijuana concede the impaired functioning that research has shown. One such site acknowledges,
The short-term effects of marijuana include immediate, temporary changes in thoughts, perceptions, and information processing. The cognitive process most clearly affected by marijuana is short-term memory. In laboratory studies, subjects under the influence of marijuana have no trouble remembering things they learned previously. However, they display diminished capacity to learn and recall new information. This diminishment only lasts for the duration of the intoxication. There is no convincing evidence that heavy long-term marijuana use permanently impairs memory or other cognitive functions.
Other studies suggest that the effect on diminished brain function is more lasting, especially for teenagers.
Thus, unlike caffeine, marijuana is not generally thought of as an empowering drug that enables you to be a more alert dad, or a more aware mother, or a more competent employee. Rather, for most users, it is a recreational escape, which produces diminished accuracy of observation, memory, and reasoning. And it may have lasting negative effects on the mind’s ability to do what God created it to do.