Hello Rossmax,
Truth is that there isn't really much known about the effects of 0.5mg finasteride. In most studies, they either study the approved 1mg or 5mg dosages of finasteride, since it's the most common dosage being used. Nevertheless, dosage at 0.2 mg already has benign effects on treating the condition -- albeit at a lower success rate compared to 1 mg per day. In terms of reduction of DHT etc., 0.2 mg is not far off from 1 mg. This means that sides, if you are susceptible to them, will develop at 0.5 mg. It also takes a while for your DHT levels to get back up, so waiting 1 day between sessions does, probably, not really lower your chances substantially.
If you are scared of side effects, doing what you are doing is fine. Some people start with .25mg daily and then up it to 1mg later. It's also common for people to do what you are doing and leave some days in between. But keep in mind that it does not mean you will not develop any sides.
If you develop sides it is advised that you stop the treatment. If not, you may choose to up your intake 0.5mg - 1mg daily or keep doing what you are doing. I would stick to your regime for around 3-4 months and assess whether you notice any sides.
