Does fast charging affects battery health or batter drain?

It affects neither battery health nor affect the rate at which the battery drains. The charger in the phone monitors internal temperature and adjusts the charge rate down if the phone is approaching a temperature that would not be good for the battery.

If you fast charge you may notice that it pauses charging at 80% to allow the phone to cool down. This essentially means that the time to charge to 100% is not significantly faster than a 7.5 watt wireless charger; the fast charging only gets you to 80%. And you will notice that Apple essentially claims that the fast charger gets you to 50% in 30 minutes. It doesn’t talk about the time to full charge, which is still 2-3 hours.

But there’s also no benefit to routinely fast charging. If you charge the phone overnight, every night, as you should, it will be at 100% when you get up in the morning even on the 1 amp charger the phone comes with. And that will last most people for the day ahead. Fast charging is for when you need the phone during a day of heavy use.

Here are more details—>When to charge your iPhone or iPad | Communities