I think if something is able to cause a loss of control then must always cause a loss of control; it wouldn't be able to do this some times and not others. If it could, what would be the explanation for the times when you kept self-control?
well, driving on a well worn tire has the ability to cause a loss of control, but doesn't do so every time I drive the car. Only when it finally blows do I veer off the highway.
If we have a drink for example this may cause a thought and urge to have another but it cannot make us decide to actually do so.
I believe that lowering inhibitions by using substances can most definitely alter our ability to make clear decisions.
Would you agree that there is an amount of substance that could alter one's decision making? If you agree that there is an amount, how can one know that amount?