This study cannot by any means be seen as having disproved the amotivational syndrome hypothesis. It has only cast serious doubt on one major study purporting to prove the existence of this syndrome. There is no doubt that some people, including some marijuana users, appear to be poorly motivated. Whether this constitutes a syndrome or not is another question. In any case, there does not appear to be any real evidence to suggest that marijuana use necessarily contributes to this condition.
External validity is more than skin deep.
Social traits of heavy hashish users and matched controls. Marijuana use and psychosocial adaptation. The amotivational syndrome and cannabis use with emphasis on the Canadian scene. Social and cultural aspects of cannabis in Costa Rica. Drugs and the whole person .