Can too much of a stimulant drug and caffeine have adverse effects (make you tired)?

Im wondering b/c Im taking phentermine (a weight loss aid/stimulant prescribed by my doctor), and sometimes I'll have an energy drink many hours after taking it b/c I feel drained (even though phentermine can stay in you for up to 12 hours). The problem is, lately if I have an energy drink after taking phentermine I feel tired. I dont get it.

Phentermine is supposed to be a stimulant drug so if I have an energy drink about 7 hrs after taking it, wouldnt it increase my energy level (even temporarily)? Im only getting really sleepy/more drained and have a spacey feeling. Whats going on?

* Iknowall: energy drinks have a lot of sugar in them.

Too much stimulant is going into your blood stream - it can actually make you very ill! Take one or the other, not both. A girl recently ended up in hopital because she drank six cups of expresso coffee within a few hours, she was very sick, disorientated and couldn't breathe!!! Be careful!

Energy drinks make you crash because the energy they give you is mostly just a sugar rush.

too much will probably kill you.

The only time you will feel tired is if your stimulants are wearing off.

All the time when your endorphines are depleted or your suffering from even minor manic depression.

Im not a doctor though.

yes it can becasue your body cant handel it. so just stick to the pills.

It's because you're over doing it and getting really low on blood sugar. Though the stimulants are keeping certain parts of your metabolism up (like fat burning) your mind is crashing because your brain cells are being deprived of sugar. If you feel like that try eating some fruit, apples are great it should help.

i my self took fastin(phentermine) with great results i lost a lot of weight. but it never made me tired or feel dranind. but i also have taken energy drinks and they are what make you the most tired i would think. if i was you i would skip the energy drink and see if it helps..