Last month, the government legalized marijuana. Many people worry that it will induce negative effects on youngsters.
Some of my friends think "generate negative effects" fits better.
Which word is correct: "induce" or "generate"?
Generate is synonymous with create - I would use this if you want to suggest that the drug will actually cause the bad effects.
Induce carries the idea of causing something to happen, perhaps bringing on something that was already there. For example, "induced labour" brings about labour in pregnant women if it does not start naturally. I would use this if you want to suggest that the drug will perhaps heighten a feeling or trigger something that was potentially already there.
However, neither of these words fit your sentence as written.
It is incorrect to say that something causes an effect on someone. Instead, you would say that it has an effect on someone.
For example:
Last month, the government legalized marijuana. Many people worry that it will have a negative effect on youngsters.
If you want to be specific about the effect on the individuals, you need to say what it is. You could then say that effect is happening in those individuals.
For example:
Last month, the government legalized marijuana. Many people worry that it will induce negative moods in youngsters.