Involved in the biosynthesis of the antimalarial endoperoxide artemisinin (Ref.7, Ref.9, PubMed:24689216, PubMed:10814821, PubMed:27488942). Catalyzes the sequential condensation of isopentenyl pyrophosphate with the allylic pyrophosphates, dimethylallyl pyrophosphate, and then with the resultant geranylpyrophosphate to the ultimate product farnesyl pyrophosphate (PubMed:8682304). Promotes anti-malarial and antimicrobial (toward Gram-positive bacteria B.subtilis and S.aureus) activities of plant crude extract probably by triggering artemisinin levels (PubMed:24689216). dimethylallyl diphosphate + isopentenyl diphosphate = (2E)-geranyl diphosphate + diphosphate (2E)-geranyl diphosphate + isopentenyl diphosphate = (2E,6E)-farnesyl diphosphate + diphosphate Binds 2 Mg(2+) ions per subunit. Isoprenoid biosynthesis; farnesyl diphosphate biosynthesis; farnesyl diphosphate from geranyl diphosphate and isopentenyl diphosphate: step 1/1. Sesquiterpene biosynthesis. Isoprenoid biosynthesis; geranyl diphosphate biosynthesis; geranyl diphosphate from dimethylallyl diphosphate and isopentenyl diphosphate: step 1/1. Expressed both in apical and sub-apical cells of glandular secretory trichomes. Strongly induced by gibberellic acid (GA(3)) leading to an increased artemisinin yield. Reduced growth and lower artemisinin levels. Artemisinin and derivatives (e.g. artesunate), are antimalarial drugs due to their endoperoxidase properties; they also display multiple pharmacological actions against inflammation,viral infections, and cell and tumor proliferation (PubMed:32514287, PubMed:32405226). Artesunate may be a promising treatment for COVID-19 mediated by the severe acute respiratory syndrome coronavirus 2 (2019-nCoV) (SARS-CoV-2) because of its anti-inflammatory activity, NF-kappaB (nuclear factor kappa B)-coronavirus effect and chloroquine-like endocytosis inhibition mechanism (PubMed:32514287, PubMed:32405226). Plants overexpressing FPS1 accumulate higher levels of artemisinin. Belongs to the FPP/GGPP synthase family.