Looking on the internet deeply has found these results:

The CEO's speech had a great effect at me. is the most popular phrase on the web.

The CEO's speech had a great effect in me. 11 results on the web	The CEO's speech had a great effect at me. 12 results on the web More popular!
Some examples and use cases from the internet:	Some examples and use cases from the internet:
No, not me. I knew they had a great football team. This dream... this nightmare soon had a great effect on my life. It's true that Shawn did say some meaningful words that had a great deal of influence on me. My parents had a great deal of trouble raising me. Because I thought we had a great time the night you got drunk and kissed me. I went out and had a great time last night, and you should be happy for me. The increase in the elderly population has had a great effect on the lives of women who, in general, when they are no longer looking after their children, have to look after their parents. It had a great part in it for me.	It doesn't look like this phrase is very popular! The search could not find any examples on the internet.

The CEO's speech had a great effect in me.

11 results on the web

The CEO's speech had a great effect at me.

12 results on the web

More popular!

No, not me. I knew they had a great football team.
This dream... this nightmare soon had a great effect on my life.
It's true that Shawn did say some meaningful words that had a great deal of influence on me.
My parents had a great deal of trouble raising me.
Because I thought we had a great time the night you got drunk and kissed me.
I went out and had a great time last night, and you should be happy for me.
The increase in the elderly population has had a great effect on the lives of women who, in general, when they are no longer looking after their children, have to look after their parents.
It had a great part in it for me.

It doesn't look like this phrase is very popular! The search could not find any examples on the internet.