Long story short

Today a PC in a homebrew campaign that I DM tried out a natural drug that he found and heard about: Flashberries. In my world it's believed to be a psychedelic drug and those who use it, become delusional: they claim to "see magic" and some say they can even interact with it. The use of arcane arts is commonly believed to not exist at all, while in actuality, arcane magic is very real (but successfully propagated against). When you consume a berry you actually are able to see the weave very clearly, and possibly even interact with it.

The party and a select few NPCs are aware of the reality of magic's existence. So after today's events, it's looking like Flashberries will play a big role in my campaign.

Question

Does D&D 5e cover any consumables that function as addictive (psychedelic) drugs? If so, does it mention positive and negative effects?

If addictive drugs already exist in any of the books I could use (some of) the mechanics as inspiration while homebrewing these Flashberries. For now I'm only interested in what the books already have to offer.

Not in the official rules

The closest that 5e has to drug rules are those for poisons, where they give some example poisons. Now obviously poisons do not give upside effects that you might expect some drugs would but they can potentially be a good place to start.

In addition to this the madness rules laid out in the DMG state:

Diseases, poisons, and planar effects such as psychic wind or the howling winds of Pandemonium can all inflict madness.

A number of the short and "long-term" madness effects would be thematically appropriate for creating drug rules. For example:

The character experiences vivid hallucinations and has disadvantage on ability checks.

and

The character suffers extreme paranoia. The character has disadvantage on Wisdom and Charisma checks.

and

The character loses the ability to speak.

Each of these could thematically be reappropriated or tweaked to provide a flavourful downside. For example losing the ability to speak could be a downside to becoming too drunk on alcohol (eg you are unable to communicate intelligibly with others, etc)

Obviously for both of these starting points you would need to come up with some appropriate benefits to counteract these downsides.

The third party product Tal'Dorei Campaign Setting contains some rules for three drugs

While not an official Wizards of the Coast product it has been written by a well regarded DM who has consulted for WoTC on a number of their D&D products in the past.

On page 55 of the Tal'Dorei Campaign Setting there is a block of rules for three homebrewed drugs (in the Dangerous Contraband sidebar)

In particular the drug Suude in that sourcebook may be something you would wish to look at for inspiration for your "seeing the weave" drug.