MSM should be taken daily, a typical dose is anything from 2g - 8g. It should be introduced slowly starting with 1g - 2g per day, then gradually increased.
Higher doses are typically necessary to experience therapeutic effects. A person suffering multiple allergic symptoms during pollen season may require more than 8 grams of MSM per day.
Results are individual, and it needs to be said there is no guarantee this will work for everybody, however some people experience improvements initially, some after a few days, others after a month. So as with every solution for health it is worth maintaining a program for at least one month.
MSM is safe for people currently taking medications. It should be noted, however, that MSM can thin blood, therefore it should be approved by a licensed doctor when used in conjunction with blood thinning medication. It is safe for children and pregnant women. MSM is not similar to inorganic sulfides, sulfites, and sulfates to which many people are allergic.