It is literally an off lable use that it is commonly prescribed for......

https://www.healthline.com/health/mens-health/sertraline-for-premature-ejaculation#safety

Mess with brain chemistry is an exaggeration. I'm talking about a type of antidepressants called SSRI's which inhibit re-uptake of serotonin which is a hormone which effects the central nervous system.

There is very little evidence of chronic use and short term potential side effects such as tremors, drowsiness, sexual distinction and weight changes as well as a few others however they are incredibly rarely harmful and are one of the most commonly prescribed medication which reflects this.

I am not telling him to "self dose" but if he wants to he can speak to his doctor and get them prescribed which is a VALID use

I am a medical student