The Entacapone element enhances the levodopa , extends the time a patient is "on", so if you are put on Stalevo after having been on Sinemet for a while it is usually done because the Sinemet is not sufficiently effective, the patient tends to have several "off " periods during the day. What has to be guarded against is that the switchover is gradual. An example to illustrate this: if the patient has been taking 125mg Sinemet, the 200mg Entacapone dose in the Stalevo tablet (every Stalevo tablet contains 200 mg of Entacapone) with probably a levodopa dose in the Stalevo tablet matching the 125mg Sinemet tablet(contains 100mg levodopa), that the patient previously took. Entacapone has an effect similar to about a 30% increase in levodopa. This could then be too much and could be the cause of dyskinesias. Slightly lowering the levodopa dose could cure this (entacapone is always a 200mg dose) Amantadine is commonly given to help with the dyskinesia.
Stalevo does not suit everybody (I did not like it). Diarrhoea is not very pleasant and could affect absorption of the drugs.