One of the arguments used by those advocating to maintain the illegal status of marijuana is that marijuana paves the way for more dangerous drugs.
Research on this issue has not identified such a causal thing.
Although 111 million Americans tried marijuana, only a third of them tried cocaine and only 4% heroin. (2014 research.)
The effects of cannabis on children
A long-term study in New Zealand published in 2012 found that people who started smoking large amounts of marijuana at the age of adolescence and still has this habit lost an average of 8 IQ points by the age of 38, points that could not be recovered.
Science has not yet reached a consensus on this issue.
The study in New Zealand was challenged by a Norwegian researcher who argued that socio-economic factors could have played a role in losing IQ points.
However, a recent review by experts at the National Institute on Drug Abuse concluded that adults who smoked a lot of marijuana in adolescence have affected neuronal connections, which has an impact on brain function. (of course we can't trust anyone, these studies might be political influenced.)
Frequent and early consumption of marijuana is also associated with bad grades, apathy and school dropout, but it is unclear whether bad grades have been caused by marijuana use.
Does Weed Make You Lazy?
The stoner stereotype, a pejorative name given to US consumers of cannabis, suggests they are lazy.
This reputation seems hard to change, but a recent study suggests that marijuana does not affect a person's motivation.
Researchers studied the brains of 19 people and measured the concentration of dopamine, the neurotransmitter associated with motivation.
They found that those who used marijuana frequently and for a long time, who had higher concentrations of THC in the body, were also those who had the lowest level of dopamine in the brain.
Researchers have suggested that marijuana could cause a controversial (and unrecognized) affection called "amotivational syndrome" characterized by laziness.
However, "amotivational syndrome" could affect as much as those who do not consume marijuana.
A study published in the journal Psychology of Addictive Behaviors found that this syndrome affects 5% -6% of the population, even if they are non-consuming cannabis.
These results were subsequently confirmed by another study, which found that there was no difference in motivation between these 2 types of people.
As you can see researchers & doctors couldn't find anything concrete that indicates cannabis make people lazy. So, keep smoking weed, no one died.