Hello.
Thank you for your query at DoctorSpring.com.
Yes, it appears to be safe. Nugenix natural testosterone does not seem to contain anything which can cause a possible adverse drug interaction with Tadalafil (Cialis).
The drugs which are contraindicated when on Cialis are Nitrates such as nitroglycerin, isosorbide dinitrate, amyl nitrate etc.
St John's wort may decrease the levels/effectiveness of tadalafil. So you can avoid supplements containing this.
I hope this was helpful.
Feel free to ask queries.
Thank you.