This summer I have the honor of working at one of the best university in Asia and we worked on the program on anabolic steroids.
Our volunteers are 12 young healthy 24-28 year old males who have normal test level[600-800ng/dL] In our studies, all subjected showed a significant drop in their own testosterone after 2 weeks of taking ONLY 20mg anavar daily, on average it drop by 78%. Most of our subject test level fall below 190 ng/dL after 2 weeks. But they don't have low test symptoms, most of them already have low test symptoms although not all of them. And their free test increase by 280% on average.
But noted, most steroid users would never consider using anavar at 20mg, a lot of guys even consider that a female dose.
We have another 12 young healthy 24-28 year old males taking 40mg tbol only. After 2 weeks, their test level drop only 26%. Most of them do not have low test And their free test only increase by 110%.
We have not finished our studies yet but so far we can conclude that anavar is definitely not a mild compound, it is very suppressive, certainly more suppressive than tbol.

I know a lot of people taking anavar only cycle and get decent result. But nobody I know get good result using tbol alone