Nah dude your cool as long a diphenhydramine (which is a antihystamine) is the only active ingrediant you are fine. Personally though, I woulndn't recommend it. Why, because when I did it i just felt tired as fuck, my body was wayyy to heavy. And I only took 12...

18 is a strong dose btw, depeneding on how much you way. If you do take it tho, make sure you have a lot of caffiene and shit. And just so you know some more information...

http://www.erowid.org/pharms/diphenh...ine_dose.shtml

http://leda.lycaeum.org/?ID=13358

Read over the second one man...It's better to make sure you got everything right, such as dosages, what u can take with it, then just doing it and making a bad mistake..