I want to get a tattoo with the phrase "drink the poison yourself," originally "Ipse venena bibas" in Latin as seen on the Catholic St. Benedict medal, but in Irish instead of Latin, as I'm very proud of my Irish heritage. I would prefer Munster Irish because that's where most of my family is from.

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I'm not a native (or entirely fluent) speaker, so be sure to wait for confirmations/corrections, especially for tattoos.

That is a literal translation of English Drink the poison yourself.
But it doesn't work in Irish.
There's an extra reflexive pronoun in English (myself, yourself, ...), put somewhere in the sentence.
But in Irish, féin is next to the subject pronoun. (D'ól mé féin an nimh. = I drank the poison myself.)
Tú féin is subject, an nimh is object. The subject must come first, next to the verb.
A subject pronoun isn't necessary in 2nd person imperative (except for emphasis), because it is a synthetic verb form, so féin is enough.

Ól féin an nimh! = Drink the poison yourself!

Because Latin bibas is subjunctive, Irish subjunctive might be used as well (instead of imperative above).
Go n-óla tú féin an nimh. (but it is less a command in Irish than in Latin: "May you drink the poison yourself.")

I thought the same thing. A curse as it were. By the way, would "thú" also be possible here?

"go n-óla thú"? No, it wouldn't
A subject "tú" is almost always unlenited: ólann tú, ólfaidh tú, d'ól tú, go n-óla tú.
The only exception is imperative mood with an extra pronoun for emphasis: ól thusa (drink you!)

Oh, that's what I was thinking. Thanks.

When I saw the request initially

ól an nimh duit féin popped into my head.

Is that possible?

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Please wait for corrections/ more input from other forum members before acting on advice

Exactly the same popped into my head. I supposed it might be argued the meaning is perhaps subtly different? (Drink it for *yourself*). But I think it's viable to be honest.