The antimotion sickness drugs protect a high percentage of individuals from becoming motion sick if the proper drug is given in sufficient dosage 1 to 2 hours before exposure, and an effective blood level is maintained throughout the required period. The stresses due to motion encountered in most civilian travel such as air, automobile and on moderate seas can be counteracted effectively by the antihistaminic group of antimotion sickness preparations. Dimenhydrinate 50mg, cyclizine 50mg, and meclozine 50mg are examples of this group. Doses can be given three times a day during prolonged exposure. If the conditions are more stressful, promethazine 25mg alone or combined with ephedrine 25mg can be given. Highly susceptible patients and very rough conditions may require hyoscine (scopolamine) 0.3 to 0.6mg with or without dexamphetamine 5 to 10mg. Promethazine or hyoscine in the above dose can be given IM as a therapeutic measure after motion sickness has developed, and both produce drowsiness which may be beneficial for the passengers but would be contraindicated for the crew.
All of the antimotion sickness drugs with the exception of dextroamphetamine and ephedrine are effective antiemetics against vomiting of toxic origins. However, the most effective antiemetics in this situation are the phenothiazines such as perphenazine, prochlorperazine and thiethylperazine. Ranking next in effectiveness is trimethobenzamide which is followed by the antihistaminic antimotion sickness drugs. Promethazine ranks with other phenothiazines as an antiemetic and is the only phenothiazine also effective against motion sickness. Morning sickness usually is self limiting but if antiemetics are required, promethazine and dimenhydrinate may be used.