The plot

[Omnipotent]

donniedarko2806412 said:

Whenever Donnie takes the pills - Frank comes.

The pills Donnie took were placebos. Meaning they have no pharmacological effect on Donnie when he takes them, so basically nothing changes in that moment.

donniedarko2806412 said:

About the sacrafice, he sacraficed himself for Gretchen

Donnie didn't have to sacrifice himself though, in the DVD commentary Richard Kelly states that Frank hits the car horn to warn Donnie to get out of bed, and he either didn't hear it, or decided not to listen. The Tangent Universe had been closed, therefore he had saved Gretchen and could have lived on. Although dying made it a much better ending.

donniedarko2806412 said:

Is Frank telling Donnie to do bad things for good reasons?

Frank is The Manipulated Dead, so he appears to Donnie using the Fourth Dimensional Construct to assist Donnie (The Living Receiver) in returning the jet engine (The Artifact) to the Primary Universe in order to save it.

[twinkle]

donniedarko2806412 said:

The pills Donnie took were placebos. Meaning they have no pharmacological effect on Donnie when he takes them, so basically nothing changes in that moment.

If the medication Donnie is on, is placebos. Why does the psychiatrist his parents to increase his medication?

because the doctor is offering a different sort of placebo to Donnie's parents by making this suggestion.

[twinkle]

donniedarko2806412 said:

Placebos are for people who think they are ill, they have absoloutley no affect on the user. Donnie is ill, he has emotional problems, the medication is probably lithium lol, to help his depression...

if i remember correctly, on the dc Richard Kelly states that Donnie is not ill, emotionally/mentally.
as always, take that for what it's worth in regards to your own interpretation .

[greedy]

as well as Dr thurman clearly tells donnie he can stop taking the pills because they are placebos