Thank you! I’ll check into Benadryl    
I know too much water could kill someone but that would require a lot of will-power because it’s slow and really painful

Anything. Even water. Anything at high enough dose becomes fatal because it has an effect on cells and the organism cannot clear it fast enough. Several gallons of water over a short period of time makes electrolytes ineffective, which causes failure of the heart and other organs. It's hard to drink that much water in a short enough span of time, but sadly it's happened. One woman did this in the late '90s on a radio show as part of a challenge. She died. 

So, pick your poison. Look into the effects of things at high doses and pick one. 

The level of pain/discomfort ranges from none to extreme depending on the substance. And success isn't guaranteed. Factors like body weight and age are important to consider. Benadryl at high dose (but not high enough) can cause horrible effects that can last for months. 

A failed suicide attempt with Benadryl (or some teen doing the Benadryl challenge...not realizing they're playing Russian roulette) can leave a person feeling like they're walking 

I mean carbon monoxide poisoning is probably the easiest thing

drinking bleach may be an ugly death, but it's effective

Not acetaminophen, though. That'll kill you, but mostly through liver failure, which isn't a great way to go.

I was here before but I just realized the easiest way probably is to get an empty syringe, fill it with air and empty the air in a vein. Dead as soon as the air reaches your heart. Don’t know who you’re trying to kill but it’s quick and doesn’t leave a dna trace or anything

Not sure about ibuprofen specifically but most things you can just get in a pharmacy do the job

I didn’t know ibuprofen could be lethal in high doses. I’ll check it out

Painkillers like ibuprofen for example, paracetamol is another one you can get over the counter. Cleaning products can be used even in low doses but that won’t be a fun death

Bear in mind that American coffee is usually considered to be weak...

Well, as TomJCharles said, EVERYTHING can be lethal in high enough doses.  I mean Oxygene in the form O3 (Ozone) instead of O2  (which is what we need to breathe) is toxic....

Here is a [video](https://www.youtube.com/watch?v=wj_AOzSSDMM) about a guy that almost inadvertially killed himself through drinking too much coffee... And you know it is a bad thing if they state "Presenting to the Emergency room, unconscious" ;)

Not immediately though.  Tyleonol overdose causes liver damage and eventually liver failure. It's a week-long if not longer process.

Tylenol PM? That would put him to sleep, at least, and he might not feel anything after that. I don’t know the amount of product needed for toxicity, though, tbh.

ETA; about 20,000mg of acetaminophen can be lethal.

Excessive drinking of water will also kill you.

I have this character and he is planning a suicide but he doesn’t want to use anything sharp. His plan rests on using any medicines that may be easily available but in high doses would kill him. Alternatively if there were something else which was lethal when ingested in high dozes, I could work with that too. Asking this here because obviously Google wouldn’t be able to give a good answer. I am sorry if I didn’t word this right or was insensitive about it.

(TW) What would be an easy to get thing, which in excessive amounts could lead to death?