I never put much faith in opiate/opioid potentiation with cimetidine, the few times I tried it with hydrocodone and morphine with negligible effect if any.
But after trying it with suboxone I am a believer, it is an amazing potentiator of buprenorphine! It not only almost doubles the subjective feeling of a dose but also extends the effects. I took 1mg of suboxone sublingually yesterday at 6pm and its now 10:30am and I am still feeling it strongly, and last night I slept like a baby when usually I suffer from insomnia. Without using cimetidine 2mg of suboxone will barely hold me and keep me well, I certainly would not be feeling it the next day.
My dosing schedule is:
1 hour before taking the sub I dose 600mg of cimetidine, then dose the sub, and then every 6 hours afterward I dose 400mg of cimetidine until I can no longer feel the sub which is usually sometime after the 24 hour mark. I still am well at this point I just no longer conciously feel the sub.
This is a big money saver with the cost of suboxone, as you can get 50 tablets of generic 200mg cimetidine OTC for under 5 dollars. Even if you have tried cimetidine before with other opiates/opioids give it a try with sub, you might be like me and able to get double the mileage out of your sub.
It appears cimetidine does have some potential side effects:
FWIW I have personally never experienced any side effects from cimetidine, but do be careful.