Effects of Various Painkillers

In my story my MC has the ability to time travel while he sleeps. His mind/consciousness separates from his body and moves freely through time. He starts out doing this unknowingly; he is unaware of it and doesn't even remember his travels like he would a dream. This uncontrolled time travel results in splitting headaches for him following each trip. When he takes painkillers - starting with aspirin - for his headaches he starts to gain control over the travels. The more he takes, the more control over them he has.

So, now that I've prefaced my question, I was wondering if anyone here knew things such as what dosage of common painkillers can kill the average person, what the side effects of too high a dosage are for them, etc.

Seems I should have went with a more concise search term/phrase. I was searching for how many aspirin it would take and kept getting nothing but people asking questions on answers.yahoo . . . people that the responders thought were suicidal.

Thanks for turning my searching in the right direction.

Edit: In response to mscelina, here's a summary of what happens in regards to the MC's use of aspirin and other painkillers.

He tries to slip a couple aspirin during work, but everyone at his office is under constant supervision and popping a couple aspirin, or any drug, harmful or not, during work isn't allowed. He explains his headache problems to his boss who demands he see a doctor to figure out what's causing the headaches.

The doctor runs an MRI to be safe because the headaches are quite severe and frequent, but finds nothing out of the ordinary. He says he'll write him a prescription for a couple medications so he can hopefully find a medication that helps more than aspirin. The aspirin was rather ineffective because, as he tells the doctor, he took two more when he was waiting to see him, for a grand total of four. The doctor says he wants to see him again in a week so they can determine where to go from there.

So far, I've been very vague about the pills he's been taking, except for the aspirin. All I've talked about is their packaging and color.

I bet bits of that are unrealistic, but I'm the sort of writer that writes from start to finish, then goes back and researches things. The reason I'm asking this question now is because without an answer it would make it a little difficult to continue with the story.

He falls and hits his head on the coffee table giving him a minor cut that left a small baseball sized pool of blood, but that is before his use of the pain killers starts to rise.

And later on he collapses to the floor, unconscious, and breathes in small bits of glass that are just centimeters away from his nose on the floor. His nose does bleed quite a bit, but he lucked out again because he had gone easy on the pain killers before this happened.

Edit: Right now, I plan for him to be put into a drug induced coma by the doctor that's prescribing him these medications in a rather careless manner. The doctor begins to see the distinct possibility that he is an addict that used him to get the prescription or he's becoming one. He becomes quite enraged by this and threatens to put him into a drug induced coma if he's given any reason to strongly believe that he really is an addict. He'll put him in a coma so he can run all the tests he needs/wants to to determine the situation and to force him into a period of about a week where he's clean. This all makes sense in the doctor's mind, at least.

Plan is, he'll give the doctor a reason to put him into the drug induced coma on purpose so he can finally be freed from all restrictions and travel through time freely. The anesthetic I plan to use for this is Ketamine. I was reading an article about a kid that has a chronic pain disorder and his only hope of treatment was to be put into a drug induced coma for all of it. It lasted about ten days and when he came out of it he had "violent hallucinations" that made his pulse and heart rate skyrocket. I don't have any plans yet for what will take place once he's out of the coma, however.

Sorry to hear about your sister. Really, I am.

No reason to apologize for the medication + overdose search suggestion. I'm grateful for it.

This doctor isn't a legitimate physician. His judgment is skewed, as made clear by how quick he is to write prescriptions for the MC. Early in the story, after the MC first visits the doctor, he sideswipes the side of the very end of the steel barrier on the side of the road. This barrier smashes through the side of his car and his arm becomes trapped between the barrier and arm rest. In the hospital after this the doctor pays him a visit and gives him more than double his earlier supply . . . a supply he hadn't even touched at that point. He did this even though the hospital planned to release him with some medications to help with the pain.

But he finally reaches a point where he stops being gullible and his frustration with himself throws all his legitimacy out the window. The MC could threaten his image, his career. Simply put, the doctor is a character with a lot of character flaws. With those flaws, he becomes more than just a minor, static character. Rather than sitting back while aiding and abetting the MC, he takes action.