How to set an hourly alarm on my iPhone?

That is not a feature of the Clock app. However, you might be able to do it in Reminders. It does a have a feature to remind you every hour.

Also, you might look at Alarmed by Yoctoville in the App Store. It has some great repeating alarm functions.

You can set medication reminders in the health app. That might be more useful as it will also allow you to track what you took when.