I recently reduced and have almost cut out stims (including caffeine). I used to take loads of stuff. I never went cold turkey, just gradually reduced my intake. It's had no ill effect on strength training or cardio for me. Infact my strength training has got better without stims. When my HR is increased now it's for a good reason, when stimulated my HR was getting high before I had put max effort in which is no good when attempting PB's on squats and deads at near your max weight.
I'm pretty fit anyway so I'm actually better off without stims for cardio.
I did get a headache when I had my first double espresso after a weeks break though 
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