For those of you who believe in the soul, how do you explain the effects of psychotropic drugs?

If the essence of who we are is a spiritual non-physical entity, how can a person’s behavior be affected by physical substances like alcohol, LSD, anti-depressants or Ritalin? Is our behavior not guided by our souls. Twelve step programs have a religious aspect, so there must be, for example, some spiritual explanation for how a normally docile person can become abusive under the influence of alcohol.