Whilst the Mézières method is a physical therapy, the Alexander technique is a psycho-physical form of re-education. Although very different in their approach, they nevertheless share some common features:

They both aim to reshape the body (even if this factor is sadly overlooked by some teachers of the Alexander technique).
They both effect a balanced redistribution of muscle tone throughout the whole body (via postural reflexes in the Alexander technique, via neuro-muscular techniques in the Mézières method).
In a way, the Alexander technique is the most fundamental of the two methods as it involves the mind as much as the body. Since ‘misuse’, in the widest sense of the word, is the main reason for the imbalance of muscle tone and the distortions and malfunctions which ensue, it could be said that the Alexander technique deals with the primary cause of our musculo-skeletal ills and various other diseased states of the body/mind . Ideally, the Alexander technique should be preventative. This is rarely the case and we all come to it with bodies distorted by years of misuse.

Although lessons in the Alexander technique can stop and even, to some extent, reverse the misshaping process, it is not as efficacious as the Mézières method in this regard. You could learn how to use yourself well and still have an imperfect shape – a good use, but one restricted by the shape of a body still encaged in stiff muscular chains (MCs). By loosening these powerful MCs and thereby resculpting the body to a greater extent, the Mézières method allows you to enjoy even greater scope and ease in the use of yourself.

The two methods complement each other perfectly.