Medicine is drugs.

Try 5-HTP as a supplement if you believe you have low serotonin levels for some reason. It's a precursor to Serotonin so if there is a chemical reason your body is producing insufficient amounts then it can help, alongside L-Tyrosine which is the same thing but for dopamine. CBD supplements, if actually legitimately containing CBD can have some anxiolytic properties.

Otherwise everything else is illegal.

Sorry honey, but under capitalism you're supposed to buy worthless shit to stave off the alienation and misery and uhh like drugs are bad m'kay. Go get into K-Pop or "Gadgets" instead, heard there's some hot spicy influencer drama in these! Lotta ads to watch! And remember: Don't think, just buy product and get excited for the next product.

You might consider an MDMA, DMT or LSD trip to figure out why you're unhappy.

Do not buy drugs on the street, they are shit quality for shitty prices, you will get ripped off. Don't buy from DNMs overseas, customs do not fuck around. In UK/West EU order to home as normal, in US order to non-home mailboxes, in East EU order to dead drops. Make sure to research how to stay safe, what markets to use, how to get Monero and how to use PGP and maybe Tails depending on OpSec risk appetite, I think Dread (ddg it with tor!) has a few guides for this.

EDIT: Make sure to set Tor to safest to disable JavaScript, you won't need it and it only creates threats.

Go for lower dosages and make sure to get powder for MDMA, it should be light brown in colour. Test it! MDMA is part stim, part empathogen.

For DMT: get a proper high end vape tank DMT vape with a 510 off a respected seller on a DNM and buy a proper mod - don't buy the crappy eGO style tanks/"carts". DMT is a pure psych, very shroom-esque but without the shroom common side effects like diarrhea and uncontrollable vomiting and lasts only 15 mins.

For LSD make sure to take some time off work or do it when you won't be disturbed in general, preferably for at least 48 hours, as a trip can last 12-16. I'd go for 100ug - tabs are often under dosed so go if brave go for 120ug, don't buy tabs with overly elaborate art as that can be a sign that more effort went into the marketing than anything else, but make sure to get a test kit to make sure it's not NBOME, that drug is nice as well but it's not LSD and vendors don't dose it properly which can kill you.

Other than psychs: Amphetamine and/or nicotine will make you happy generally, but unless you have ADHD the effect may be too negligible to be worth it.

If your source of unhappiness is anxiety then you can take an anxiolytic like a benzodiazepine. Do not do that.

There's also Alcohol and Opioids but these barely do anything honestly when it comes to actual happiness. I would not do THC in an unhappy state, it's like 75% anxiety and hunger.

Or you can try therapy, but that shit never worked for me, turns out the world is just shit and my life was shit as a result, taking drugs helped/helps me cope with that and I try to improve my material circumstances as much as possible, I've never really had mental health issues though I just had shit mental health due to my material conditions so YMMV and GL, the first step to fixing an issue is identifying there is an issue. Try to identify what the issue is next.