Stimulants and smart drugs. Diet, exercise and a healthy sleep schedule is probably your best bet though. When I was using heroin, I found that taking high doses or piracetam every morning and having two cups of coffee made a HUGE difference too btw. Check out stuff a little on the milder end of the stims too, such as Modafinel or whatever its called.
Ninae - Yea, I know it is. It is supposed to be the same thing. However, when I was taking what I am sure 100% was Neurontin, even 350mg without a tolerance would have me feeling like I was drunk. However, when I got was was generic gabapentin, it literally did nothing, at least nothing even approaching what I experience from the brand name Neurontin. I have also taken Lyrica, and it's certainly strong than either ime. I never understood what happened with the disparity between my neurontin/gaba experiences... a bad batch or something, or maybe my biology was fucked up at the time or something? who knows...
Taking 15 instead of 5mg would just get you more fucked up, increase respiratory depression, increase your nod and if you don't have any tolerance lead to a very dangerous situation.