@TheUltimateFixx makes a very important point. Pedialyte is my favorite, but Gatorade or something similar is fine too. If you don't have that or can't get it, it's easy to make your own. Here is the recipe I found a while back that I like to use and tell people about.
1 liter of clean water
6 level teaspoons sugar
1/2 Teaspoon salt
You can throw some fruit juice in there if you want it to taste like something.
People who use Methamphetamine tend not to eat. We would normally get many of the needed electrolytes through our diet. What this means is regular water with nothing else added to it is only going to go so far. If you've been sweating, moving and etc. for many hours, you're going to be really deficient in these things. My point is that regular water is not going to be capable at rehydrating you in the way you really need, especially if you're not eating anything.
People don't realize how shitty being dehydrated makes you feel. When I started using Amphetamines in High School, I would get high, be glued to something for 6 hours and not eat or drink anything. The comedown was often much worse than it needed to be. I started forcing myself to drink a glass of water every hour with a timer on my phone. It truly made a difference for me.
I'm not sure if you're referring to a comedown or you're referring to a Methamphetamine addiction that will entail a withdrawal period. If it is just a comedown, eat/hydrate and use whatever makes you comfortable. The classic choice would be a Benzodiazepine. I would take a Benzo when the high was over, but I was still too stimulated to actually sleep. I'd take a Benzo and would be able to start sleeping sooner and avoid that negative time. There isn't any harm in it so long as you're not combining the Benzodiazepine with other depressants.
Cannabis, if you like Cannabis, would be helpful. It can stimulate your appetite allowing you to eat a few bites of food without too much discomfort. Also, it's a great sedative with essentially no negative health consequences.
If you like Gabapentin (Neurontin), sure you could take some of that without too much worry. Everything else is really up to you. My best advice though would be Benzodiazepines. The only thing I really would be against would be Alcohol. We all know how taxing Alcohol is on the body, including dehydration. If you factor in the increased dehydration, you can get into trouble pretty easily. I've had some truly terrible hangovers as a result of combining stimulants and Alcohol.
I hope this helps.
