The psychomotor effects of seven commonly used drugs, both licit and illicit, have been examined in human volunteers when given alone and in combination with alcohol. The drugs include A9-Tetrahydro- cannabinol (the main psychoactive principle of marihuana), two minor analgesics (aspirin and paracetamol), a preparation for the treatment of the common cold (Contac 500), a drug (allopurinol) taken for the treatment of gout, and disodium cromoglycate which is used to relieve the symptoms of asthma and allergic rhinitis.