Does taking melatonin for insomnia really work?

My family member has trouble falling asleep, and if they wake up in the middle of the night, it's even harder to fall back asleep. They were prescribed sleeping pills, but they only took half a pill, and they said it didn't help at all.

I'm considering taking melatonin because people around me say it helps with sleep.

There are so many types of melatonin that I don't know which one to buy.

There are melatonin supplements that you can buy, and there are also melatonin prescriptions available at hospitals.

Has anyone had their sleep quality improve after taking melatonin? I'm really curious to know if melatonin is really effective.

 
I'm also concerned about side effects. Some people report feeling extremely drowsy or lethargic upon waking up in the morning. Are these side effects common? I'm also wondering if it could affect depression or other neurological conditions. Could you please advise me on how to take melatonin safely?