The present invention relates to a method for preparing a Cannabis plant &Dgr;9-tetrahydrocannabinol isolate from a crude solvent extract of Cannabis plant material. The invention relates further to a Cannabis plant THC isolate comprising &Dgr;9-tetrahydrocannabinol, Cannabinol (CBN) and/or Cannabidiol (CBD) and to a pharmaceutical composition comprising the Cannabis plant THC isolate.