Another objection to amateur prescription of medicine is the fact that most drugs have more than one effect. In addition to their main action they have others, subordinate or ordinarily less marked. These minor effects may be serious in some cases. Many headache remedies, for example, affect the heart; a dose that is harmless for a normal person may be strong enough to injure seriously a person with a weak heart. A doctor, and a doctor only, is competent to decide when and in what quantity medicines will be beneficial, because he alone understands both the condition of the patient and all the possible effects of the drug. In no circumstances should medicine prescribed for one person be taken by another. This rule seems obvious enough; yet every day people pass on their pet remedies to friends. Some medicines deteriorate after standing, and others grow stronger; nevertheless, medicine supposed to have cured a cough or a tonic supposed to have strengthened some member of the family after an attack of grippe is cheerfully administered months later to another member of the family, who, to make matters worse, may differ in age, strength, and probably in the nature of his sickness. Drugs are expensive, and it is considered economical to use them up; measured by lost time and impaired health such practices may be anything but thrifty. Cathartics, tonics, and various drugs to relieve pain and sleeplessness are among the remedies most commonly taken without medical advice. Enough has already been said about constipation to indicate proper hygienic treatment, but another warning should be given against habitual use of cathartics. Many of these drugs are irritating; even when not irritating, they are harmful, since the body depends more and more upon the drug to do for it what it should be enabled to do for itself, by remedying the original cause of the trouble. Licorice powder, cascara, saline cathartics such as Seidlitz powders and Rochelle Salts and some others are harmless for occasional use, if occasional is not too liberally interpreted. Tonics are poor substitutes for proper diet, rest, and fresh air. Using them may be likened to beating a tired horse; the horse goes faster, but he is not really stronger. In some emergencies the horse must go faster and there is nothing to do but beat him, and in some cases the tonic should be given; these, however, are cases for a doctor to decide. People persist in taking tonics because they are unwilling or unable to rest, or otherwise to change their ways of living.