Getting high from a drug does have bad effects, and not just long term ones either. That good feeling is a rush of dopamine, and when you do that constantly your body stops producing its own dopamine that it would natrually. Basically, the more you use the drug the more difficult it becomes to stop using it, because you're no longer getting your own body's naturally produced happy pill.
The doctor who gave you this in order to improve your mood is, to put it lightly, a
terrible doctor.
There are other drugs out there, as well as herbs, that specifically work to improve mood that don't give a high. Those are the kinds of things you want to be taking to help you out with this.
Please, please wean yourself off this stuff, or if you find it too hard then look for a good doc that'll help you. This ilness is really rough, and I don't blame you for wanting to check out of reality for a bit, but you do not want to pass the years in a fog, enslaved to a drug. That isn't life. Reality is going to be even rougher because of your misuse of the drug, but it's worth it, and you'll find people are ready and willing to support you through that difficult process.