In English it’s a long i (/ˌaɪ.bjuˈpɹoʊ.fən/), so you’ve got it correct! In most other languages it’s closer to what English speakers think of as a long E (i.e. how most languages pronounce the letter i). But unlike you, the designer of this sweatshirt made two mistakes.

First, the second character is pu instead of bu, so it starts off as ipu instead of ibu. The two are differentiated by the diacritic in the upper right:

ブbuプpu

Second, the エ (e) should actually be a small ェ, so it actually says ipuprofuen (adding an extra vowel):

✔フェ ❌️フエ

I know these things might seem subtle if you don’t speak Japanese, but I’m just baffled that whoever made this shirt failed at copy-pasting the word from a dictionary. But then again, the katakana I see on shirts is more often wrong than right, so it’s apparently harder than you’d think.

my man!