what does euphoria exactly mean when it comes to be the adverse effect of some CNS drugs?

I looked it up in the dictionary, and it says "a feeling of well-being or elevation".so i don't really understand it.
Answers:
Euphoria is an intense feeling of elation. In laymans terms, an extremely happy or giddy feeling. It is the "high feeling" of some drugs. It isnt always a good thing as it may be the very thing the medication is trying to combat or, as another person said, it can be followed by serious depression. It isnt always harmful however. Discuss it with your doctor if you think you are experiencing euphoria. He or she may be able to switch your medication to something you can tolerate better.

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does adverse mean negative?
if it does then how euphoria can be something bad?
anyway euphoria is just pure happiness usually with no obvious reason to be happy

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It is a psychological sensation; an intense sense of happiness.And in response to the above answer.
How can euphoria be negative?
It can be bad because in many cases euphoria is a state that eventually passes and is followed by very serious depression.

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Euphoria IS a feeling of elation and extreme well being, almost a high.As an adverse reaction to a CNS drug, it is dangerous, because this person may hallucinate, think they are indestructible, do dangerous things, that may harm themselves or others- it can also have the Down side, of crash and burning, coming to the extreme opposite, of Depression, etc, when coming off the medication.

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