Can you tell me the most common side of finasteride and their likelihood of occuring?

Side effects of finasteride relate to lowered testosterone. This would include difficulty in getting or maintaining an erection.   In young males side effects are not frequent, in my experience.  In male patients over 40, it is more prevalent.  In my experience it is also reversible when the drug is discontinued.  If there is concern, start with the generic finasteride; since generic medications are often a bit weaker than their name brand counterparts.  I would also stick to the 1 mg strength tablet.  Some people get the higher dose, 5 mg tablet, which would be more potent and have more of a testosterone blocking effect.

The most common side effect of Finasteride is decreased libido. Still not common, maybe 2%, but it scares many patients. There is a lot written about "post Finasteride syndrome" but as clinicians we rarely see it. If it looms large in one's mind, there is an alternative in Minoxidil tablets. See a hair restoration doctor for the best advice.

The most common side effect of finasteride is probably slightly increased hair shedding in rhe first 3 months that the drug is used.  To answer your question about the risk of gynecomastia - that has been estimated to be between 4 to 10 out of every 1000 men who use the drug. If one is concerned about gynecomastia, I advise patients to take photos to monitor. Gynecomastia is usually one sided but can be both sides. It typically starts a few months down the road but can be much more delayed. Many men have pain or tenderness before the gynecomastia is noticeable. The risk of erectile dysfunction is dependent on age but is around 2% on average.