The right answer is an antiparasitic drug (like metronidazole).
Giardiasis is an intestinal infection caused by Giardia lamblia, a microscopic unicellular parasite.
The parasite that causes giardiasis is lodged in the intestines of humans and infected animals.
In some cases, giardiasis disappears spontaneously in about 1 month. Other people need to take antiparasitic drugs (eg, metronidazole) to shorten the duration of the infection and kill the parasite.