How to tell how long a drug stays in your system?

[WorldWarMe]

Someone told me today to find out how long a drug stays in your system you're supposed to take the half-life and multiply it by 2, for example Tramadol's half life is 5-7 hours, so it would stay in my system for 10-14 hours.

Is this true, or is that just how long that the drug is active in your system?

My main goal is to find out how to know the length that a drug stays in your system, and also how to find out how long it's active in your system, if there's even a difference.

The reason I'm asking is because I took Tramadol around 34 hours ago and was wondering if I would be able to take 5-HTP without having an interaction.

Thanks in advanced to whoever answers my question

 

[fm1983]

Sake of argument:

You take 2mg of tramadol, with the half-life being 5hrs. 5hrs after initial dose, 1mg will remain. 5hrs after that, .5mg will remain. 5hrs after that, .25mg will remain. and so forth on, every 5hrs, whats left will be cut in half.

My take anywho, and how I interpret half-life. Anyone can feel free to correct me if I completely off base.

Anyways, I had a heavy oxy habit around 150mg a day. If I last dosed on a Friday, I could take a drug test Monday, and pass. Did it multiple times. The half-life is roughly 4hrs or so.

 

[Psychedelic Jay]

No, it's half of the initial dose, not half of what's left in the blood.

Initial dose of 200mgs, 7-8 hours later 100mgs, 7-8 hours later it's gone. So 14-16 hours later, it's out of your system. So, you are good to take 5-htp.