I'm on a medication that is a stimulant and raises my base heart rate. Can I then work out at a higher heart rate?

In general, perceived exertion is your best guide for what you are trying to do in the gym regardless of medications. Our base heart rate actually changes daily depending on many things. When you workout, you may feel extremely motivated (let’s say if you got a really good night’s sleep or something exciting happened) and thus you will go harder and have a higher average heart rate. If you are fatigued or depressed, you will feel less motivated and not achieve nearly as high an average heart rate.

It also depends on what the medication is. If the medication elevates your heart rate to the point of being very noticeable and uncomfortable, you should notify your physician. Many medications as well as common soft drinks, foods and supplements can elevate our heart rate. These typically elevate the heart rate only slightly and the effects are temporary. Therefore trying to work out at a higher heart rate to compensate for a slightly higher resting heart rate will not produce equitable results. That’s why using perceived exertion is a better guide of your exercise intensity. If you are concerned that your medication is having a negative side effect, the best thing to do is exercise as you normally do and keep a close watch for any overt changes.