Mario Dell'Agli, who led the study at the University of Milan, even says that a medication based on horny goat weed may as effective as Viagra, with an additional benefit of lesser side effects.
He has revealed that his team undertook the study to establish the potential of the four plants as alternatives to the famous blue pill.
Viagra's active compound, sildenafil, promotes male erection by inhibiting an enzyme called phosphodiesterase-5 (PDE5), which controls blood flow to the penis.
In lab experiments, Dell' Agli and his colleagues tested the four plants to determine their efficacy in inhibiting PDE5.
The researchers observed that just one of the plants Epimedium brevicornum, also known as horny goat weed and Bishop's Hat had an effect.
The findings of the study confirm suggestions that a compound found inside the horny goat weed, icariin, is a PDE5 inhibitor.
The research team extracted icariin from the plants, produced six modified versions of it, and tested them on PDE5.
Dell'Agli said that there was one compound that worked "as well as Viagra". He added that a drug made from that compound could also cause fewer side effects than Viagra.
Besides inhibiting PDE5, sildenafil affects other phosphodiesterases that are essential to sight and heart function, and thus people with heart problems are not advised to take the blue pill. Viagra takers often suffer disturbances to their eyesight.
The new compound, however, appears to be safe in terms of such health effects, according to the researchers.
Dell'Agli reckoned that the compound developed by his team might take about a decade to reach the market, because it has to go through lengthy clinical trials.
"(Meanwhile) if people eat horny goat weed, I think it can be beneficial because it contains icariin. But it will not be as effective as Viagra," says Dell'Agli.
A research article on the study has been published in the Journal of Natural Products.