Before going to a homoeopathic physician many people fear that their trouble would be aggravated. The most common question asked is that do your medicines first increase the complaint? Considerable misconceptions exist about this type of reaction.
Dr. Hahnemann has clearly explained this in the aphorisms 154- 160 in the ORGANON.
Aphorism 154 reads: If the antitype constructed from the list of symptoms of the most suitable medicine contain those peculiar, uncommon, singular and distinguishing (characteristic) symptoms, which are to be met with in the disease to be cured in the greatest number and in the greatest similarity, this medicine is the most appropriate homoeopathic specific remedy for this morbid state; the disease, if it be one of not very long standing, will generally be removed and extinguished by the first dose of it, without any considerable disturbance.

The reaction to the medicine would be different in acute and in chronic diseases:
In acute disease any aggravation is seldom seen unless there are tissue changes or the disease has progressed a lot pathologically, or it has lasted very long and is very severe. If this were the state then sharp aggravation, great prostration, violent sweating, exhaustion, vomiting and purging following the action of the remedy are seen. These severe reactions are necessary for recovery. Such a state in acute disease where it has gone many days without a remedy and a great threatening is present would be to an acute disease what many years would be to a chronic disease of long standing. If the disease has reached to a stage where tissue changes have occurred, then we see striking aggravations; even aggravations that cannot be recovered from, such as we find in the advanced forms of tissue changes e.g. where kidneys or lungs or liver is destroyed.

It is important to understand whether the disease is acute or chronic. In acute diseases the similimum would cure without any serious aggravations, whereas in case of diseases where tissue changes have taken place aggravation would first occur followed by relief. This is due to the reaction of the vital force or the vitality to eliminate the disease from the body. Where there is deep-seated septic condition, where pyaemia must be the result, you will find sometimes vomiting and purging.

This enables the vital force to react and bring the economy to order. This order, which is attended by reaction, as it were, commences a process of house cleaning. The vital force does it itself, the drug does not do it; if a crude substance is used it is the action of the drug, of course, but the action of the dynamic drug is to turn the economy into order. In case of a chronic disease, which has not ultimated to tissue changes, no such aggravation is seen, unless it be a very light exacerbation on the symptoms, and that slight exacerbation of symptoms is of a different character. It is the establishment of the remedy as a new disease upon the economy instead of the reaction, which corresponds to a process of house cleaning. Elimination must take place, as we know, probably from the bowels, or stomach, by vomiting, by expectoration, or by kidneys, in those cases where everything has been suppressed.

Dr. Kent gives the example of a case of paralysis of a limb from neuritis. He says that suppose we administer a remedy that is exactly similar and goes right to the spot. The patient develops tingling and creeping like crawling interiorly of ants, sometimes from which he cannot sleep for days and nights. This is due to the reaction of nerves of the affected part, as they are called into life, into activity.

The other example is of a child, who has lain in a stupor for a long time, from inaction of the brain, the tingling that comes in the scalp, in the fingers and the toes, is dreadful, the child screeches and cries, turns and twists, and it requires an iron hand on the part of the doctor to hold that mother from doing something to hush that cry, for just so sure as that is done that child will go back into death. All this is the reaction established by the remedy, which increases the blood circulation to the affected parts. The dead nerves come into action and if anything is done to stop this reaction then it can revert the condition. That part has been benumbed and dead, and when circulation takes place in the part in order to repair its tissue we have reaction, which is attended with distress. If the physician cannot look upon that and bear it he will have trouble. If he thinks it is an indication for another remedy he will spoil his case.

Thereafter he writes: We must discriminate between that which is reaction and that which calls for a remedy. These things are only seen in homoeopathy, never in any other practice. Sometimes the physician will be driven to the end of his wits dealing with these reactions. It is sometimes a dreadful thing to look upon, and the physician may be turned out of doors. Let him meet it as a man; let him be patient with it, because the ignorance of the mother or the friends can be no excuse for his violation of principle, even once.

The reaction of the patient to the remedy administered depends upon the state of vitality. If the vitality is in an active state, then the reaction of the economy would be stronger and if the vitality is feeble then no such marked aggravation will be seen. The cause for this is that a feeble constitution does not produce enough symptoms for selection of exact similimum, thus the reaction established is not so strong. Whenever a remedy is administered, it establishes a drug disease on the economy, which is stronger than the first, but similar in manifestation to it. This enables the vital force to react again and enables it to extinguish the original malady.

Dr. Kent cites an example wherein he states that, say you get a patient that is destined to go into consumption, a merely suspicious case. You administer the right remedy and a violent reaction comes, a foreshadowing of what he will go through years from now if the remedy does not cure him. A shocking condition will come upon him; he may be frightened and come back and tell you that that was an awful dose of medicine, poison etc. That is the remedy disease, those are the symptoms of the remedy foreshadowing the future of that case, because if that remedy was not similar enough to him it could not do such things, and it is because of the similitude of his state; and he may only have those symptoms in shadow. But the remedy cannot give him symptoms that he has not. It cannot give him symptoms that are not related to him except in those cases that are called oversensitives. Oversensitives, you know, are such as are capable of proving everything that comes along. You must know whether the patient is oversensitive and proving the drug, or whether he has a vigorous constitution and is getting an aggravation. The remedy will be exaggerated in oversensitives and sometimes in those of weakly constitution, especially those with a very narrow receding chin, those who have sunken eyes, those who have senility marked in the eyes.

In aphorism 155 Dr. Hahnemann mentions that, I say without any considerable disturbance. For in the employment of this most appropriate homoeopathic remedy it is only the symptoms of the medicine that correspond to the symptoms of the disease that are called into play, the former occupying the place of the latter (weaker) in the organism, and thereby annihilating them by overpowering them; but the other symptoms of the homoeopathic medicine, which are often very numerous, being in no way applicable to the case of disease in question, are not called into play at all.

This is because the similar remedy when administered only affects the parts that are affected or weakened at that moment. The dose is excessively minute and is much too weak to affect the other parts which are not homoeopathic to the case, and can allow only the homoeopathic symptoms to act on those parts of the organism that are already most irritated and excited by the similar symptoms of the disease. Thus the affection of the vital force is changed to a similar but stronger medicinal disease whereby the original disease is eliminated.

About the repetition of the dose Dr. Kent quotes,
You will find as a general thing in acute diseases, that if a slight aggravation of the symptoms comes in few minutes, you will hardly ever think of giving another dose. The remedy is so similar and searches so thoroughly that it is hardly ever necessary to repeat it. There are circumstances when it is necessary to repeat, but this is so difficult to teach, and so difficult to lay down rules for, that the only safe plan is to begin cases without repetition, to give a single dose and wait, and watch its effects. I very commonly give in vigorous, typhoid fever patients medicine in water, because it is a continued fever; but I watch and wait, giving it several days, and the slightest sign of action of the remedy causes me to stop it always. I never vary from that. In a fever where the patient is feeble, to gain an immediate reaction that should never be done.
In a remittent fever the reaction may come in a very few hours, and the one dose should be the rule, while in a typhoid the reaction will seldom come in a few hours. It is a matter of a few days, and hence the repetition is admissible. In typhoids that are somewhat delicate never do such a thing. The more vigor there is in a constitution the more the remedy can co-operate with that vigor to bring about a safe and quick action.
The more feeble the patient the more cautious you should be about using the smallest dose you can give. In many chronic diseases it is possible to bring about a reaction in the first night hence the danger of repeating the remedy. If the delirium subsides, or moisture comes on the skin, and he slumbers placidly, the medicine should never be given beyond such a state. There are times in diphtheria when the repetition of the remedy will kill, and there are times when repetition will save life. I hope some day to be able to discover the principles.

Thus, repetition of the remedy is solely on the physician decision. He is the judge when he takes a case about the course of action. So, it is important for him to have complete knowledge of the human kind, his vitality and his disease, principles and laws of homoeopathy and last but not the least about the medicines he is administering and the potential that they carry. Then and then only can he bring about a cure and relief to the one in distress.

Aphorism 158 states:
This slight homoeopathic aggravation during the first hours a very good prognostic that the acute disease will most probably yield to the first dose. That a natural disease can destroy another by exceeding it in power and intensity, but above all things by its similarity, is the whole truth and nothing but the truth. So that when this slight aggravation occurs you will seldom, if ever, have to give another dose in an acute disease. When this aggravation does not come, when there is not the slightest aggravation of the symptoms, and the patient appears to be gradually better after the remedy, then it is the remedy shows that it has not acted upon the same depth; and that relief may cease in the case of an acute disease, and when that relief ceases the reaction has ceased and then another dose of medicine is correct practice.

Relief that begins without any aggravation of symptoms does not last so long as in an acute disease as when an aggravation has taken place. A slight action of the remedy over and above the disease is a good sign. Again you will find that if your remedy was not perfectly similar you will not get an aggravation except in oversensitive patients, and then it is a medicinal aggravation. When you find that you get no aggravation of symptoms in a good vigorous constitution, none at all, very often your remedy has been only partially similar and it may require two or three of such partially similar remedies to finish the case.

If you will observe the work of ordinary physicians you will observe that they give two or three remedies to get their patients through where a master gives but one.
 Aphorism 159 states that, The smaller the dose of the homoeopathic remedy, the slighter the apparent aggravation of the disease, and it is proportionately of shorter duration.

This was written at the time of Hahnemann experience with what might be called small doses, ranging from lower potencies to the 30th and seldom much higher. He had had ample experience with the 30th, and occasionally with the 60th, but not with the tremendous turmoil that comes with the very high attenuations. It reads in the correct translation of it: the smaller the dose is of the homoeopathic medicine, the less and the shorter is the aggravation in the first hours. It might be considered to mean an apparent aggravation, or an apparent aggravation of the disease. Now Hahnemann observes, as you will find amongst several of his writings, that the disease itself is actually intensified and made worse by the remedy, if the remedy be precisely similar, but if we pass away from the crudity of the medicine, ranging up towards the 30th potency, we get a milder action and it has a deeper curative action, and the smaller the dose of the homoeopathic medicine the less and the shorter is the aggravation.

Dr. Kent cites an example of a very young woman, twenty years old, who was sent a dose of Bryonia, to be taken dry on the tongue. However, she dissolved it in water and was taking it at the end of the second day, when he was sent for, at which time she seemed to be going into pneumonia. She had a dry, harsh cough. He stopped the Bryonia and next morning she was well. This has been seen a great many times when the medicine was similar. If the medicine is not very similar, only partially similar it yet may be similar enough to cure, but you will not see the results that have been spoken of; but when you make accurate prescriptions, and are doing your best work, you will see these things in the very best constitutions.

Of course, the explanation is that the patient is as sensitive to the medicine that will cure her as to the disease he or she has. Diseased states then are made worse by unnecessary repetition and by the dose not being small enough, that is, by the dose being very crude. The third, fourth and sixth are dangerous potencies, if you are a good prescriber, if you are a poor prescriber, you will demonstrate but little of anything. You will naturally go to the higher and higher potencies for the purpose of departing from what seems to be a poisonous dose.