Can a mantra or sound be used as a medicine?

The answer is yes. The difference between a Mantra and a sound is that Mantra sound is an energized sound with medicinal values. There are many aspects of Mantra as a sound:

The type of sound matters. It is well?known that chanting of vowel sounds produces interleukin?2 in the body, which has the same action as that of aspirin and works like a natural painkiller. Chanting of nasal consonants produces delta activity in the EEG and has similar action like tranquilizers. Chanting of other consonants has different actions in the body. For example, chanting of LUM reduces fear, VUM reduces attachments, RUM reduces doubt, YUM increases love, HUM increases truthfulness and AUM non?judgmental activities.
Mantra sounds can be vibratory or non?vibratory. Vibratory sounds use nasal consonants and vibrate bones beginning from mandible, spine, and the automatic plexus lying along the spine. Chanting of nasal consonants leads to a parasympathetic state.
Chanting of mantra is associated with reduced respiratory rate, which leads to parasympathetic state of the body. Ideally, the respiratory rate should be reduced to 4 per minute and then continue it for next 20 minutes i.e. 80 breaths in 20 minutes. This can be done by chanting, for example, the whole Gayatri mantra in one respiratory cycle.
How one chants also matters. The yogic way of chanting is when the mind is in mantra or the chanting. This leads to deeper relaxation.
Understanding the meaning of the Mantra you chant also matters. If you do understand the meaning, the chanting benefits will be more. Foreigners do not understand the meaning of Indian Mantras but yet they get benefits. But if they chant with understanding the meaning of the Mantra, the health benefits will be more.
Chanting a mantra with its meaning in the mind invokes the power of intention. It?s like getting connected to any search engine on the internet and typing your query. Your consciousness in the body is the internet and the intention the search button.
Chanting a mantra with its meaning in the mind also results in emotions and expressions, which have an added advantage.
Overtone chanting has additional benefits. The new sound heals not only those who are chanting but also those who are listening and bystanders.
Group chanting is more powerful. If 1% population chants together, rest 99% also gets the benefits.
One can also do distance healing by chanting at a far distance. The only way one can explain this is by understanding consciousness as an internet cum social site model. Each one of us has our page in the internet (soul) as well as a page in the cloud internet (spirit). All our pages are connected with every person in this earth through the cloud internet. People can chant at a distance and their audio file with intent automatically gets posted on their soul internet and the cloud internet. The person for whom we pray by chanting gets the benefit whenever he is connected to the cloud internet.
During chanting, the mind may be distracted. Continuously chanting of Mantra for 12 seconds means concentration, 12�12 seconds is contemplation and 144�144 seconds is meditation. So by concentrating on the object of concentration, the mantra, one can avoid diversion of the mind.
The intensity or the loudness of the chanting sound also matters. Higher the loudness, less will be the effects. Japa meditation involves two hours of Mantra chanting to get the benefit. In a non Japa meditation, these benefits can be acquired in 20 minutes. Thoughtless chanting is more powerful than verbal Mantra chanting. Vipasana is chanting without Mantra where you are just aware of the breath and one has to do this type of meditation for hours together to get the benefit.
During Chautha or Teravi (mourning period), Mantras or prayers are chanted for one hour. This helps relax the mind, shifts one from sympathetic to parasympathetic mode. In the initial 15 minutes, there is sympathetic overactivity and the person is restless. As the time passes, parasympathetic state takes over and by the time one hour is over, parasympathetic state is at its full blown activity and at that time getting connected to cloud internet is easier.

Only those who are connected to the dead person and want to get distressed attend the full one hour of Chautha ceremony. These people have empathy for the deceased person. Those who wish to express sympathy, mostly show up before or after the Chautha ceremony to complete their formality.

In Chautha, we say that Bhagwan Uski Aatma Ko Shanti De. God will forgive him only if the soul is destressed, which can happen only if there are some non?fulfilled desires and these desires will always be linked to a particular person. Therefore, only those who have guilt will feel that the deceased person?s soul is not at rest.

In a Chautha ceremony, one can only remove this guilt in the parasympathetic phase towards the end of the Chautha ritual and seeks forgive and forgiveness.
In different religions, this has different implications. In Hinduism, we only attend Chautha of whom we know but in Islam people attend the mourning ceremony of people whom they not even know. They believe in mass prayers and pray for the soul of the deceased person. In Islam this mass prayer message gets written on the cloud internet and has mass effect in the community.

In Islam, a person usually says Mein khuda se tumhare liye dua mangunga. It is possible for them as they offer Namaz five times in a day and when they ask for Dua for someone they put the intent in the cloud internet which can be retrieved by others.

In Christians, it is different. The dying patients or the relatives ask the doctors and others to pray with them and not only for them.