Nope, not at all. The only detrimental effects weed can have is if you smoke before your brain is full developed (so before 19-21 years of age, around there), in which case it can cause your brain to develop slower. Most people start smoking around 16 or so, and you'll notice those are the ones that usually adhere to the stereotypes (lazy, unmotivated, etc) as opposed to someone who started smoking towards adulthood who usually operate perfectly, whether sober or otherwise. But of course there's exceptions to everything. In reality though, the plain facts are Marijuana is one of the most beneficial substances available, and can act as a medication for almost anything. That's why I get really, really mad when people try taking shit based off of what they hear rather than doing the research themselves