There are several things to consider in taking Propecia (finasteride). First off, brand name and generic do not matter. Brand name proscar 5mg is never dispensed as it is available generically. Propecia 1mg is currently brand name only so it must be dispensed this way until it's patent expires (next 2 years). In any case, they are all the identical chemical, just in different potencies. Steer clear from names like finpecia etc. from out of the country as their potency and content is not verified. Luckily in the USA we have the FDA.
Secondly, your weight and muscle mass is an important indicator of the appropriate dose you should take. Why? Because finasteride is highly lipophilic (fat soluble) and distributes widely into the tissues. A person who is obese is going to lose a lot more drug while it is traveling through the bloodstream into the tissues. A thin muscular person will retain the drug in the bloodstream and it will be more likely to get to the site of action, hence will require a lower dose. The dose that was FDA approved for ALL people is 1 mg daily. Why 1 mg? Because this is the dose that is effective in most everyone. Keep in mind we live in on average an obese population, so this dose is too high for many averaged size people. Clinical studies have shown that as little as 0.2mg daily were effective in blocking conversion of testosterone into DHT and stoping hair follicle death.
Next, lets talk about the half life. On average it is about 6 hours, about half of the drug is excreted from your system in 6 hours. Typically, a drug will be completely excreted in about 4-6 half lives, so in finasterides case about 24 hours. However, looking at our data, a dose of 0.2mg was effective in some people. For simplification, lets say the entire 0.2mg gets into your bloodstream upon taking 0.2 mg orally (it doesn't as the bioavailability is much less than 100% but its an arbitrary number). Therefore, 6 hours after taking the dose (or longer due to time it takes for absorption), you will have a blood level of 0.1mg. After 24 hours it would be 0.025 mg left over. This was the lowest point that the drug has shown effectiveness (AKA trough level). So technically a dosing schedule that would work in a lot of people is 0.2mg daily. For more simplification lets call it 0.25mg daily. Theoretically, 0.5 mg every other day would give you the same trough and would be acceptable.
Now here's the tricky part. Although the above listed doses would give you similar trough levels, the peaks would be much different. Taking the higher 0.5 mg every other day, your peak blood levels would be higher than taking the drug more frequently, in our example 0.25 mg every day. What risk does this cause? Higher peak levels are associated with greater side effects. Therefore it would be better to be on a daily regimen than every other day, however with the formulations that are available it would bed difficult to cut the pieces this small and have an accurate dose.
Personally, I titrated the dose to the lowest effective dose for me. I take 0.25 mg every day. However for me it was easy as I compounded the drug into capsules. This dose works great for me as I have a low BMI and low body fat composition, and I have minimal risk for side effects.
The reason I want the lowest effective dose and not the safe dose (1 mg daily FDA approved) is because finasteride is a chemical that changes hormone levels in your body and is potentially dangerous. When testosterone blocked from conversion to DHT, high circulating levels have no choice but to be converted into Estrogen by the enzyme aromatase. And in reality you do need some DHT for your body to carry out normal functioning. I would not recommend its use in patients less than 18 years old as it has the potential to interfere with normal development.
That being said, it is currently all we have to prevent one important aspect of hairloss, so we need to consider the risks and benefits carefully.