Can I take anti-malarial medication to prevent dengue?

No, anti-malarial medications really don’t give any reliable protection against dengue fever.

Malaria comes from a parasite carried by the Anopheles mosquito, while dengue is a viral infection spread by the Aedes mosquito. Preventive drugs such as Malarone or Doxycycline focus on the malaria parasite; they’re essentially useless when the problem is a virus. Preventing bites still is the only effective preventive approach for dengue; that point matters a lot. Also, Sri Lanka was declared malaria-free by the WHO in 2016, so anti-malarials are generally unnecessary for travel there, and people should plan accordingly.