You will never get a totaly clear head. there are two main active chemicals in maryjane.
THC (Tetrahydrocannabinol) gets a user high, a larger THC content will produce a stronger high. Without THC you don't get high.

CBD (Cannabidiol) increases some of the effects of THC and decreases other effects of THC.
Indica is more of a Body high because of more CBDs, and sativa is more of a head high with higher contents of THC and not much CBDs. But all this can be effected by the length of Flowering and curing.